Apparatus and method for low flux photocatalytic pollution control

ABSTRACT

A new method for design and scale-up of photocatalytic and thermocatalytic processes is disclosed. The method is based on optimizing photoprocess energetics by decoupling of the process energy efficiency from the DRE for target contaminants. The technique is applicable to both low and high-flux photoreactor design and scale-up. The low-flux method is based on the implementation of natural biopolymeric and other low-pressure drop media support for titanium dioxide and other band-gap photocatalysts. The high-flux method is based on the implementation of multifunctional metal oxide aerogels and other media in conjunction with a novel rotating fluidized particle bed reactor.

[0001] This invention relates to processes and apparatus forphotocatalyidc, thermocatalytic or combined photo and thermocatalytictreatment of fluids containing undesirable compounds for pollutioncontrol and energy production applications and was made with thefinancial support of the U.S. Department of Defense, Naval SurfaceWarfare Center, Indian Head Division under contract numberN00174-91-C0161, Office of Naval Research under Augmentation Awards forScience and Engineering Research Training Program, contract numberN00014-93-1-0907, and Army Research Office under Defense UniversityResearch Instrumentation Program, contract number DAAH04-96-1-0295, andis a Continuation-In-Part of Provisional Application 60/107,236 filedNov. 15, 1998, which is a Continuation-In-Part of ProvisionalApplication 60/081,324 filed Apr. 10, 1998.

FIELD OF THE INVENTION

[0002] Examples of treatable streams include, among others, ventilationmakeup air, ambient air, air from stripping and off-gassing operations,soil vapor extraction (SVE), airborne matter (e.g. organic particulate,biogenic and microbial matter) and process vent gas, wastewatertreatment off-gas, liquid effluents (e.g. wastewater, industrial andagricultural runoff) containing at least one undesirable or otherwiseunwanted compound. Moreover, this application presents a holisticapproach to the design of the high performance photo and thermocatalyticsystems that possess:

[0003] i—Rapid species mass transfer to and from the active sites of thecatalyst

[0004] ii—Uniform transport of thermal and radiant energy to the activesites of the catalyst

[0005] iii—Decoupling of the conversion efficiency from processintrinsic energy efficiency.

[0006] iv—Minimal pressure drop.

BACKGROUND OF THE INVENTION

[0007] As environmental regulations become progressively more stringent,new techniques and approaches are needed for dealing with difficultcontaminants. For example, the required destruction and removalefficiencies (DREs) for some environmental pollutants, such as toluenediisocyanate (TDI), dioxin, dibenzofurans and polychlorinated biphenyls(PCBs) are extremely high. Conventional methods such as carbonadsorption or liquid scrubbing are not a complete remediation solutiondue to the fact that they simply transfer contaminants from one medium(i.e. water or air) to another (i.e. solid carbon or scrubbing liquid).On the other hand, incineration and catalytic thermal oxidation presenttheir own limitations. For example, the widespread production and use ofchlorinated compounds in the industrially developed countries hasresulted in large amounts of halogenated organic contaminants to seepinto the soil, water and air. Incineration and even thermocatalyticoxidation of wastestreams containing halogenated compounds in many casesproduce emission of products of incomplete combustion (PIC) such asdibenzofurans, dioxin and other pollutants that are known or suspectedcarcinogens. It is to be understood that in the terminology of thisapplication “target species/compounds” denote those entities containedwithin the contaminated stream that are targeted for completedestruction and removal.

[0008] The past two decades has seen rapid growth and promulgation ofnew remediation technologies. In particular, a class of pollutioncontrol technologies known as the advanced no oxidation processes (AOPs)has been the focus of much research and development. Among AOPs, thosethat employ ultraviolet (UV) radiation in conjunction with activeoxidants (i.e. ozone, hydrogen peroxide, hydroxyl radical, superoxideion radical, etc.) to accomplish mineralization of the target organiccontaminants are of special interest. Generally, UV/AOPs arecharacterized with respect to the type of either the catalyst andchemical reactions involved (i.e. homogeneous vs. heterogeneous) orlight source employed (i.e. solar vs. artificial).

[0009] In general, UV/AOPs for treatment of the hazardous organiccontaminants (HOCs) in fluids (both gas- and liquid-phase) comprise thefollowing steps:

[0010] In the first step, an organic contaminant (hereafter-called“primary reactant” or “target compound”) that is adsorbed on thecatalyst surface or resides within the fluid reacts to form products(hereafter termed “intermediate” or “secondary” products).

[0011] In the next step, the secondary products react to form otherproducts (hereafter called “tertiary products” or “final products”) thatcan be regarded as more benign, safer, or less detrimental to health andenvironment. The tertiary products are formed through a sequence orstepwise reaction scheme and an effective way to obtain tertiary orfinal products is to use specially engineered catalytic reactorsdisclosed in this document.

DESCRIPTION OF THE PRIOR ART

[0012] It is generally recognized that the UV-based AOPs do notuniversally enjoy high process energy efficiencies. This realization hasmotivated many researchers to test the concept of integrated or hybridprocesses. In this approach, several processes are combined to produce ahybrid system that is capable of treating contaminants in the wastestream at much higher overall process energy efficiency and reducedlife-cycle costs than each of individual processes, alone. This isespecially true in applications where the initial concentration of thetarget compound may vary wildly in the course of the treatment process.

[0013] A good example is ethanol emission (in air) from somepharmaceutical product dryers. Ethanol concentration in the productdryer varies during a typical cycle by two orders of magnitude. Also,hybrid processes can be used in certain applications where valuablechemicals (e.g. acrylonitrile monomer, solvents, etc.) are emitted inthe effluent that can be recovered. Yet another example involvestreatment of the energetic materials. It is known that thephotocatalytic treatment and mineralization of 2,4,6-trinitrotoluene(TNT) in aqueous media is difficult. However, once partially oxidized,many microorganisms can readily metabolize the partial oxidationproducts. Here, a UV/AOP is combined with another treatment process(i.e. biological) to achieve a much higher process efficiency. Examplesof surrogate processes employed in the prior art include bioremediation,electron beam, thermocatalytic oxidation, activated carbon or syntheticadsorbents, UV/H₂O₂ and UV/O₃, to name just few. Alternatively,performance improvement can be made at the catalyst/support level, usingmultifunctional catalytic media, i.e. capable of acting as bothphotocatalyst and thermocatalyst.

[0014] It is to be understood that, in the terminology of thisapplication, “media” or “catalytic media” denotes the combination ofphotocatalyst(s) and its/their supporting base material(s). Most basematerial(s) of the prior art simply provide(s) a structural support forthe active catalyst(s) used and do not normally partake in the reactionsor provide other known functions. Examples include, but not limited to,U.S. Pat. Nos. 4,892,712, 4,966,759 and 5,032,241 to Robertson et al.;U.S. Pat. No. 5,126,111 to Al-Ekabi et al.; and U.S. Pat. No. 5,035,784to Anderson et al. However, it is possible to have a multifunctionalmedia that is both photocatalytically and thermocatalytically active.The rationale for using a multifaceted media will now be described.

[0015] Consider a UV/AOP that employs a high power light source such asa medium-pressure mercury lamp (MPML). MPMLs generate large amounts ofthermal radiation, at relatively high temperatures. Even when alow-pressure mercury lamp (LPML) is used as the source of UV light,considerable amount of low-level waste heat is given off. For example,according to vendor specifications, a standard 65 W Voltarc^(R) lamp(G64T5VH), converts less than 40% of the input electrical power toemitted light in the form of 254-nm radiation. The electric to UV energyconversion efficiency is lower yet for fluorescent black light (lessthan 25%) and medium pressure mercury lamps (less than 15%).

[0016] It is generally recognized that only a very thin layer on thephotocatalyst surface can actually be excited to enter photocatalyticreactions. For most active photocatalysts, the physical thickness ofthis layer or skin does not exceed few microns. This is due to the factthat UV radiation is completely absorbed within a skin only few micronsthick on the exposed photocatalyst surface. On the other hand, thermalradiation can penetrate deep into the supported catalyst and basematerial. The fact that most target species can also be adsorbed intothe deep layers of the photocatalytic media (inaccessible to UV butaffected by thermal radiation and heat) encourages the use ofmultifunctional catalysts capable of utilizing both heat and lightemitted by medium and high pressure UV lamps. Thus, a multipurposecatalyst can comprise a base material that acts as both a thermocatalystas well as support structure for the photocatalyst. Alternatively, adual catalyst may be used that can function as both thermocatalyst andphotocatalyst, simultaneously. It is also possible to implement athermocatalyst and a photocatalyst separate but together, in series.

[0017] The use of combined photo and thermocatalytic action as in anintegrated media is known in the prior art. Examples include Muradov, N.Z., Tabatabaie-Raissi, A., Muzzey. D., Painter, C. R. and M. R. Kemme,Solar Energy, 56, 5 (1996) 445-453; and Fu, X., Clark, L. A., Zeltner,W. A., and M. A. Anderson, J. of Photochemistry and Photobiology, A:Chemistry 97 (1996) 181-186, among others. Muradov et al. describe aphoto/thermocatalytic method for selective oxidation of airbornevolatile organic compounds (VOCs) including nitroglycerin, ethanol andacetone. The light source used was a low-pressure mercury lamp. Thecatalytic media employed was TiO₂ modified with silico-tungstic acid(STA) and platinum. Fu et al. describe photocatalytic degradation ofethylene in air at elevated temperatures over sol-gel derived TiO₂ andplatinized TiO₂ particulates, irradiated with a fluorescent black lightlamp. Both studies report improved performance at elevated reactiontemperatures without platinization of the photocatalyst.

[0018] The use of bandgap semiconductors such as titania (TiO₂), ZnO,ZrO₂, CdS, etc. and their various modified forms as the gaseous andaqueous phase photocatalysts is well known in the prior art. Forexample, TiO₂ particles (anatase crystalline form, in particular) arereadily excited upon exposure to near UV radiation (wavelengths belowapproximately 400 nm) producing electron/hole (e⁻/h⁺) pairs on thesemiconductor surface. The recombination of e⁻/h⁺ pairs has theresulting effect of reducing the process quantum efficiency. Therecombination can occur either between the energy bands or on thesemiconductor surface.

[0019] It has long been recognized that certain materials such as noblemetals (e.g. Pt, Pd, Au, Ag) and some metal oxides (e.g. RuO₂, WO₃, andSiO₂) facilitate electron transfer and prolong the length of time thatelectrons and holes remain segregated. The electrons and holes act asstrong reducing and oxidizing agents that cause break down of the targetcompounds via formation of active radicals on the photocatalyst surface.The following groups of reactions describe the excitation of titanialeading to the generation of active radicals:

TiO₂ +hv→h ⁺ _(vb) +e ⁻ _(cb)  (i)

h ⁺ _(vb)+OH⁻ _(ad)→^(•)OH_(ad)  (ii)

e ⁻ _(cb)+(O₂)_(ad)→(O^(−•) ₂)_(ad)  (ii)

(O₂ ^(−•))_(ad)+H₂O→OH⁻ _(ad)+(HO^(•) ₂)_(ad)  (iv)

h ⁺ _(vb) +e ⁻ _(cb)→heat (recombination)  (v)

[0020] Reaction (a) occurs within the TiO₂ lattice. When TiO₂ absorbs aUV photon, represented by hv, having an energy equal to or greater thanits bandgap energy, electrons (e⁻ _(cb)) shift to the conduction band,and positively charged “holes” (h⁺ _(vb)) remain behind in the valenceband. Energy is related to wavelength by Planck's equation:

E=hc/λ

[0021] Where: E is the bandgap energy (eV), h is Planck's constant(6.6256×10⁻³⁴ Js) and c refers to the velocity of light (2.998×10¹⁰cm/s), and λ is the wavelength (nm) of radiation.

[0022] Assuming bandgap energy of 3.1 eV for TiO₂, a thresholdwavelength of about 400 nm is obtained. TiO₂ will absorb light having awavelength equal to or lower than this value. Once holes and electronsare photogenerated they move about the crystal lattice freely in amanner described as the “random walk.” The random walk results in theelectrons and holes either recombining (thermalizing) per equation (v)or reaching the surface of the catalyst to react with adsorbed speciesand produce reactive radicals as indicated by equation (ii), (iii) and(iv).

[0023] An important factor in controlling the rate of electron-holerecombination on the photocatalyst surface is the size of catalystparticles. The smaller these particles are the shorter the distance thatcharge carriers must travel to reach the surface and the larger theexposed catalyst surface area is. Photocatalysts having X-ray diameterof only a few nanometers and BET surface area of many 100 s m²/g arecommercially available (e.g. ST-01 and ST-31 grades titania produced byIshihara Sangyo Kaisha, LTD of Japan).

[0024] The rate of recombination of holes and electrons is a function ofthe catalyst surface irradiance. Prior art teaches that higher thesurface irradiance, the greater the rate of recombination of electronsand holes (Egerton, T. A., King, C. J., J. Oil Col. Chem. Assoc., 62(1979) 386-391). Prior art also teaches that only one of the process(ii) or (iii+iv) is the rate-limiting step. The process involving theother radical completes the reaction and preserves the overall chargeneutrality. Thus, it is generally recognized that the hydroxyl radicalformation is the rate-limiting step. The rate of surface reactions willthen be equal to r=k_((c+d))[h⁺ _(vb)]. The rate of hole formation isk_(a)q_(i), where q_(l) denotes catalyst surface irradiance(quanta/s/cm²). The rate of electron-hole recombination is then k_(e)[h⁺_(vb)][e^(•) _(cb)]=k_(e)[h⁺ _(vb)]². When q₁ is high, a large number ofelectrons and holes will be generated, and Egerton and King have alreadyshown that: r=kq_(i) ^(½). At low values of q_(l) when surfaceconcentration of holes, [h⁺ _(vb)], is relatively small, therecombination term will be negligible and r=k_(a)q_(l). The surfaceirradiance value (hereafter called “Egerton-King threshold”) at whichthe reaction rate transition from q_(l) to q_(l) ^(½) (1 to ½dependency) occurs is q_(EK)=2.5×10¹⁵ quanta/s/cm² (at λ=335, 365 and404 nm).

[0025] The q_(EK) can be calculated for two commonly used UV lightsources (i.e. low- and medium-pressure mercury lamps). For the LPMLs andMPMLs q_(EK) is approximately equal to 1.95 mW/cm² (for λ=254 nm) and1.36 mW/cm² (for λ=365 nm), respectively. In order to limit the rate ofrecombination of electrons and holes and maximize the photoreactorperformance, it is necessary to limit the catalyst surface irradiance tolevels at or below the Egerton-King threshold. The rate of surfacereactions, r, is proportional to q_(l) ^(m), where m varies between ½and 1. To increase the rate of surface reactions for target pollutants,it may be necessary to allow q_(l) to exceed q_(EK) under certainconditions. Therefore, in a practical situation, the requirement for anefficient utilization of the photogenerated charge carriers must bebalanced against the need for optimum rate of the surface reactionsinvolving the primary and secondary reactants that produce desirablefinal products. In general, this requires a careful photoreactor designthat allows uniform irradiation over all photocatalytic surfaces at alevel that is as close to q_(EK) as possible and optimum rate ofconversion of surface-borne target species to desirable final products.

[0026] Just like radiation and heat transfer, transport of the primaryreactants to and final products from the catalyst surface affect thephotoprocess performance. The reactor engineering is closely coupled tothe choice and configuration of the media and the type of light sourceused. A proper photoreactor design should provide for uniform irradianceon all catalytic surfaces as well as effective species mass transport toand from the catalyst active sites. Mass transfer limitations affect theprocess efficiency, as all target species must reach theactive/activated catalyst surface before any reaction can occur. Forprocess streams containing very low concentration of contaminants, thetransport effects are even more pronounced. In general, photoreactordesigns fall into one of the following three categories:

[0027] 1. Most photocatalytic reactors/processes of the prior art belongin here. The Category I photoreactors possess good mass transfer butgenerally poor radiation field characteristics. FIGS. 1a, 1 b, 1 cdepict several examples from prior art depicting photocatalyst-coatedmonolith, photocatalyst-coated panel, and baffled annular photoreactor,respectively. Other examples include Australian Patent PH7074 toMatthews; U.S. Pat. No. 3,781,194 to Juillet et al.; U.S. Pat. No.4,446,236 to Clyde; U.S. Pat. No. 4,774,026 to Kitamori et al.; U.S.Pat. Nos. 4,888,101 & 5,736.055 to Cooper; U.S. Pat. Nos. 4,892,712,4,966,759 & 5,032,241 to Robertson et al.; U.S. Pat. No. 5,126,111 toAl-Ekabi et al.; U.S. Pat. No. 5,045,288 to Raupp et al.; U.S. Pat. No.5,069,885 to Ritchie; U.S. Pat. No. 5,480,524 to Oeste; U.S. Patent5,564,065 to Fleck et al., U.S. Pat. No. 5,683,589 to de Lasa et al.;U.S. Pat. No. 5,790,934 to Say et al.; and U.S. Pat. No. 5,030,607 toColmenares, to name just a few.

[0028] 2. Poor mass transfer but mostly uniform catalyst surfaceirradiance, e.g. annular photoreactor design (no internals, catalystcoated on the outer wall).

[0029] 3. Poor mass transfer and nonuniform catalyst surface irradiance,e.g. externally lit annular photoreactor (no internals, catalyst coatedon the inner wall).

[0030] As noted before, a good photocatalytic reactor design shouldprovide for a uniform near q_(EK) catalyst surface irradiance andtemperature as well as no mass transfer limitations. This requiresconsiderable process and reactor optimization effort prior to scale-up.Experimental techniques involving the measurement of the radiativeproperties of materials including photocatalysts are generally verycomplex and time consuming. Likewise, computational methods foranalyzing radiative exchange among surfaces and between surfaces andgases even under the simplest of conditions are very difficult toexecute. This so because the equation of transfer, in general, is of thecomplex integro-differential form and very difficult to solve. Othercomplexities including chemical reactions, species mass transfer, etc.further complicate photoprocess/reactor analysis and optimization.Therefore, it is not surprising that the prior art offers very little inthe way of photocatalytic process and reactor analysis, modeling,optimization and scale-up. When it comes to the photocatalytic reactorand process engineering and design, the prior art methodologies aremostly pseudo-quantitative, semi-empirical and intuitive, in nature.

[0031] For example, it has long been recognized that providing means forgeneratina and enhancing turbulence in the flow generally improvesspecies mass transfer to and from the catalyst surface active sites. Anexamination of the prior art reveals that many articles such as ribs,fins, pleats, beads, chips, flaps, strips, coils, baffles, baskets,wires, etc. have been conceived, used and patented for generating mixingand turbulence in the flow and generally improve mass transfercharacteristics of the reactors. Thus, using flow agitating articles or“internals” to enhance the contaminant mass transfer to the catalystsurface is more or less intuitive. But, the effect of internals or“turbulators” on the radiation field within the photoreactor seems to beless obvious and seldom fully appreciated. Often, methods used in theprior art to eliminate mass transfer intrusions adversely affect theextent and uniformity of radiation received on the catalyst surface,within the same photoreactor. One example is the annular photoreactorhaving internal baffles such as one shown in FIG. 1c. The U.S. Pat. No.5,683,589 (de Lasa et al.), U.S. Pat. No. 5,069,885 (Ritchie), U.S. Pat.No. 5,116,582 (Cooper), and U.S. Pat. No. 5,790,934 (Say et al.) are allvariations of this basic configuration. The catalyst surface irradiancefor the photoreactor configuration of FIG. 1c has been carried out bythe subject inventor and results are given in FIG. 2.

[0032] Results of FIG. 2 indicate that, if internals must be used toimprove mass transfer, it is more advantageous to design thephotoreactors in such a way that the bulk of catalyst resides on thereactor wall. This requirement limits the number and proximity ofinternals, in general, and baffles, in particular, that can beincorporated into the photoreactor. It can be seen that for the bafflespacing smaller than one baffle diameter (see U.S. Pat. No. 5,683,589 tode Lasa et al. and U.S. Pat. No. 5,790,934 to Say et al.), the surfaceirradiance (as a fraction of the lamp's radiosity) is lower on reactorwall than the baffle surface. Furthermore, results of FIG. 2 indicatethat the point of diminishing return with respect to the magnitude anduniformity of the surface irradiance is reached at inter-baffle spacing,L, of about 10 times the sleeve diameter (D_(i)). The fact that thebaffle spacing equal or greater than L=10D_(l) is necessary forachieving a uniform irradiance results in the wall irradiance levelsthat are well above the q_(EK). Moreover. the L/D_(l)=10 requirementresults in inter-baffle distances that are unsuited to proper fluidmixing. These and other effects combine to make the use of mostinternals or turbulators generally undesirable.

[0033] Another important but poorly understood phenomenon within thephotocatalytic reactors of the prior art is the light refraction andreflection effect. FIG. 3 depicts an annular photoreactor with threelinear UV lamps, 120° apart, along the reactor axis. FIG. 4a-4 b depictthe lateral variation of the wall irradiance as a function of thepacking radius, r_(p). All three lamps are lit and data are shown fortwo r_(p)/r_(o) values (0.333 and 0.452) and a range of baffle spacing,denoted by L/r_(o), from 0.76 to 6.10. On the same graph, the analyticalpredictions for the lamp as a diffuse line source emitter are alsogiven. The measured wall irradiance dips at all locations havingshortest radial distance to the lamp axis. This effect is due to therefraction and blocking of UV rays from the posterior lamps. When therefraction effects are all accounted for, the experimental data are ingood agreement with the analytical and model predictions. This is shownin FIG. 5 for one of the baffle spacing of the arrangement of FIG. 4a,i.e. L/r_(o)=6.10. This example clearly shows that refraction andreflection of light is likely to affect irradiance distribution withinthe catalytic matrix of several photoreactor designs of the prior artsuch as the U.S. Pat. Nos. 4,892,712, 4,966,759 & 5,032,241 (Robertsonet al.) and U.S. Pat. No. 5,126,111 (Al-Ekabi et al.). It can now beappreciated that the configuration of the catalytic media and design ofthe photocatalytic and thermocatalytic reactors must be kept as simpleas possible. This requirement is in addition to ones discussed before(i.e. having good mass transfer and radiation field characteristics).

[0034] Moreover, a photoreactor design that yields a uniform irradiancedistribution over all its catalytic surfaces, does not lend itself tomass transfer intrusions and has a simple design that is readilyscalable, can still be affected by low process energy efficiency. Thisis so because, in one-pass reactors, the process energy efficiency iscoupled with the conversion efficiency (or process DRE). When very highprocess DREs are required, the transport effects lead to process energy,efficiencies that are well below the maximum realizable. This so-called“coupling effect” adds another complexity to the design ofhigh-performance photocatalytic and thermocatalytic reactors. Thus, oneobject of the present invention is to teach a novel method formitigating the adverse effects of coupling on the performance andenergetics of single-pass photocatalytic, thermocatalytic or combinedphoto- and thermocatalytic reactors.

[0035] An examination of the prior art reveals that six distinct typesof catalytic media arrangement have been used, to date. For the sake ofdiscussions here, they are termed as the Type 0, Type I, Type II, TypeIII, Type IV and Type V, of which Types O-II and IV are substantiallyphotocatalytic and Types III and V are substantially thermocatalytic,albeit multifunctional media.

[0036] In Type 0 photocatalyst/support configuration, a suitablecatalyst such as titania is used in colloidal form without any supportor base material(s). Examples of Type 0 media include, among others,U.S. Pat. Nos. 5,554,300 and 5,589,078 to Butters et al.; U.S. Pat. Nos.4,888,101 and 5,118,422 to Cooper et al.; and U.S. Pat. No. 4,861,484 toLichtin. A sub-category of Type 0 media includes, among others, U.S.Pat. No. 5,580,461 (Cairns et al.). Cairns, et al. employ a combinedprocess that includes, in addition to colloidal titania photocatalysis,a surrogate process based on the use of adsorbent material. Thecontaminated fluid is first contacted with a particulate adsorbentmaterial that physically adsorbs the target compound. The contaminantloaded adsorbent is then separated from the fluid and brought intocontact with aqueous slurry of a suitable photocatalyst. The use ofadsorbent material implies, implicitly, that the technique is moresuited to treatment of processes in which the adsorption of targetspecies on the photocatalyst surface is the rate-limiting step. This isnot generally the case, especially in the vapor-phase processes wherethe rate of reaction for one or more surface bound species (primary orsecondary reactants) control the overall rate of the reaction and finalprocess outcome. It is therefore desirable to simplify the treatmentprocess by eliminating the surrogate adsorbent in favor of amultifunctional catalytic media (catalyst and support combination) thatis both a good adsorbent as well as a good photocatalyst.

[0037] In Type I photocatalyst/support arrangement, the catalyst (oftena modification of the anatase crystalline form of TiO₂) is immobilizedor bonded onto a ceramic, glassy (e.g. fiberglass mesh, woven glasstape, etc.) or metal oxide (e.g. silica gel), metallic (e.g. stainlesssteel), or synthetic polymeric (e.g. plastic) substrate. Examples ofType I media include, among others, U.S. Pat. No. 5,564,065 to Fleck etal.; U.S. Pat. No. 5,449,443 to Jacoby et al.; U.S. Pat. No. 5,045,288to Raupp et al.; U.S. Pat. No. 5,069,885 to Ritchie; U.S. Pat. No.4,446,236 to Clyde; U.S. Pat. No. 5,736,055 to Cooper; U.S. Pat. No.5,683,589 to de Lasa et al.; U.S. Pat. No. 5,790,934 to Say et al.; andU.S. Pat. No. 5,374,405 to Firnberg et al.

[0038] In Type II media configuration, impregnated glassy mesh/matrix orporous ceramic monolith or beads, metallic and metal oxide substrates(in the form of plates, beads, etc.) are employed as the photocatalystsupport to which titania is bonded utlizing a method known as the“sol-gel technique.” There are many variations, but, a typical processfor preparing colloidal sols and corresponding media is discussed in“Photocatalytic Degradation of Formic Acid via Metal-Supported Titania.”H. Y. Ha and M. A. Anderson. J. of Environmental Engineering, March,1996, pp. 217-18. the contents of which are incorporated herein byreference. First, a solution of titanium isopropoxide mixed with dilutenitric acid in a ratio of H₂O/Ti(i-Pro)₄/70% HNO₃=300/30/20 ml isrefluxed at 80 degrees centigrade for 3 days. The resulting colloid isthen concentrated with a vacuum rotary evaporator. The final titaniaconcentration of the colloid becomes 1.06 mol/L at pH 0.8. The mediasupport used were stainless steel 304 plates and tin (IV) oxide-coveredglass. The stainless-steel plates were pretreated by firing at 450degrees centigrade for 2 hours to produce a metal oxide layer. A PMWspinner system was used to produce uniform titania layers on thesupport. The support was spun at 2500 rpm for 30 seconds. The coated gelwas first dried at room temperature and then fired at a temperature thatmay vary between 300 and 600 degrees centigrade with a heating rate of 3degrees centigrade per minute. Typical dwell times were about 2 hours.The process is repeated until the desired catalyst thickness isobtained.

[0039] Type II catalyst/support examples include, but not limited to,U.S. Pat. Nos. 4,892,712, 4,966,759 and 5,032,241 all to Robertson etal.; U.S. Pat. No. 5,126,111 to Al-Ekabi et al.; and U.S. Pat. No.5,035,784 to Anderson et al. In Type I and Type II arrangements, thesubstrate has no known function other than providing physical andstructural support for the photocatalyst.

[0040] Type III catalyst/support configuration is a variation of theType I media that involves synthesis and use of metal oxide aerogels,most prominently SiO₂ aerogels doped or co-gelled with other transitionmetal oxides such as titania to produce photochemically activecatalyst/support material. There are many methods and variations of thebasic technique used for preparing high porosity metal oxide aerogels.In general, preparation of metal oxide aerogels and porous glassescomprise a two step process in which a condensed metal oxideintermediate is formed. From this intermediate compound aerogels areprepared having any desired density, clarity and UV transparency,thermal insulation capacity, moisture and mechanical stability.

[0041] Two general reactions have been used to make earlier metal oxideaerogels. In the process of U.S. Pat. No. 2,249,767 to Kistler, first ametal alkoxide is hydrolzed by reacting with water and an alcohol in thepresence of a reagent (e.g. NH₄OH). Second, the hydrolyzed metalundergoes a condensation reaction to form a metal oxide gel, from whichan aerogel is made by supercritical fluid extraction of the solvents. Animprovement to the Kistler's method is given by the single-step sol-gelprocess of the U.S. Pat. No. 3,672,833 to Teichner et al. Teichner'smethod, employs a silicon alkoxide tetramethoxysilane ortetraethoxysilane which is hydrolyzed by one to ten times stoichiometricquantity of water with an alcohol in an acidic, neutral or alkalienvironment. This is followed by the condensation reaction in which thehydrolysis products polymerize to form a wet gel. In Teichner's method,the alcohol is removed directly from the wet gel at above supercriticalpressure and temperature point of the alcohol. It should be noted thatany metal that can form an alkoxide, which includes essentially theentire periodic Table of elements, could be used to make an aerogel.Examples include: silicon, germanium, zirconium, titanium, iron,magnesium, boron, cerium, lithium, and aluminum, to name just few.

[0042] Further improvement upon the techniques developed by Kistler andTeichner has been made recently through many new syntheses methods.Examples include, among others, U.S. Pat. No. 5,030,607 to Colmenares;U.S. Pat. Nos. 5,275,796 and 5,409,683 to Tillotson et al.; U.S. Pat.No. 5,538,931 to Heinrichs et al.; U.S. Pat. No. 5,718,878 to Zhang;U.S. Pat. No. 5,759,945 to Carroll et al.; U.S. Pat. No. 5,766,562 toChartha et al.; and U.S. Pat. No. 5,753,305 to Smith et al. As anexample, the properties of the low-density silica aerogels made bymethod of the U.S. Pat. No. 5,409,683 (Tillotson et al.) is describedand incorporated here by reference in its entirety. The density of thesilica aerogels prepared by this method varies typically betweenapproximately 0.0015 g/cm³ and 0.8 g/cm³. Representative refractiveindex of the Tillotson silica aerogels are in the range of 1.0005 and1.170 when measured at a wavelength of 632.8 nm. Light transmittance istypically greater than 85% at 632.8 nm. For a monolithic silica aerogel,2 cm thick, a bulk density of 0.05 g/cm³ and prepared by the method ofU.S. Pat. No. 5,409,683, the light transmittance at λ=400 nm istypically 45%. The porosity, expressed as the percentage of open spacewithin the total volume, falls in a range between 64% and 99.9%. Thespecific surface area of these silica aerogels is in the range of 450 to1000 m²/g. The properties of silica aerogels given here by reference tothe U.S. Pat. No. 5,409,683 to Tillotson et al. are also typical ofother metal oxide aerogels (e.g. titania) prepared by similartechniques.

[0043] A typical Type III media most useful to the practice of thepresent invention can be made by methods of the U.S. Pat. No. 5,409,683to Tillotson which is incorporated here by reference. In Tillotson'stwo-step method, a high purity metal (e.g. silicon, titanium zirconium)alkoxide is mixed with a hydrolysis rate reducing alcohol (such asmethanol, ethanol or propanol), an additive (e.g. acetylacetone, aceticacid and hydrogen peroxide) and a sub-stoichiometric amount of water toform a solution. If silicon metal is used, the suitable alkoxide istetramnethoxysilane (TMES). Likewise, for titanium metal, the desirablealkoxide is titanium isopropoxide. The metal alkoxide solution is thenreacted with a suitable acid catalyst (e.g. hydrochloric acid) to forman oligomeric mixture of a partially condensed metal intermediate and areaction produced alcohol. This is followed by the removal of alcohol bydistillation and evaporation. The next step involves adding anonalcoholic solvent such as acetonitrile or acetone to the partiallycondensed metal intermediate to form a non-alcoholic solvated condensedmetal intermediate which is then reacted with a second catalyst (ammoniaor fluoroboric acid) and mixed. The amount of catalyst regulates the pHof the solution and determines the rate of gel formation. After mixingis completed the condensed metal oxide product is cast that is, pouredinto a mold to form a wet gel. The gelation takes about 72 hours andcarried out at room temperature. The nonalcoholic solvent and anyreaction-generated alcohol is then removed by supercritical extractionusing liquefied carbon dioxide, chlorofluorocarbons (freons) or propane.More recently, methods have been developed for preparation of both bulkand thin film aerogels in which the gel drying is carried out undersubcritical conditions (Jochen Fricke, “Superexpansive Gels,” Nature,vol. 374, pp. 409-410, 1995). Another important development involvesrapid aging technique for aerogel thin films (U.S. Pat. No. 5,753,305 toSmith, et al.).

[0044] An important application of the metal oxide aerogels is their useas heterogeneous catalyst and support structure for chemical processesinvolving oxidation, epoxidation, hydrogenation, reduction, synthesis,etc. As such, co-gelled metal oxide aerogels such as titania-silicaaerogels and transition metal aerogel-supported catalysts (e.g.platinum, nickel, cobalt and copper supported on silica aerogel) arewell known in the art. For example, U.S. Pat. No. 5,538,931 toHeinrichs, et al. teaches a process for preparing a supported catalystcomprising a transition metal such as palladium or platinum on anaerogel (e.g. silica) that is most useful as a hydrogenation catalyst.U.S. Pat. No. 5,766,562 to Chattha et al. discloses a method forpreparing titania aerogel supported precious metal (e.g. platinum,rhodium) catalyst useful for the automotive exhaust gas (NO_(x),hydrocarbons and carbon monoxide) emission control. U.S. Pat. No.5,030,607 to Colmenares teaches a method for preparation of UVlight-transparent silica aerogels doped with photochemically activeuranyl ions (UO₂ ⁺⁺) for photocatalytic synthesis of short chainhydrocarbons in a fluidized bed photoreactor.

[0045] In Type IV photocatalyst/support media a photocatalyst (e.g.doped and undoped modifications of TiO₂, CdS, etc.) is deposited bybonding or cementing onto the fabric of a modified or unmodified naturalor synthetic polymer material. Examples for polymers of natural origin(or biopolymers) include wood, paper, kozo, gampi, Kraft lignin, andwoven cotton, kenaf, linen, wool, etc. (U.S. Pat. No. 5,246,737 toMuradov and U.S. Pat. Nos. 5,604,339 and 5,744,407 to Tabatabaie-Raissiet al.).

[0046] Finally, the Type V media includes the broad field ofmoderate-temperature (approximately 150-350° C.) thermal oxidationcatalysts. Of particular interest to practice of the present inventionis a sub-class of the moderate temperature thermal oxidation catalyststhat include supported transition metal oxide catalysts and cationmodified zeolites as dual function sorbent/catalyst media. For example,U.S. Pat. No. 5,414,201 to Greene discloses a combined sorbent/catalystdual function media which removes dilute VOCs, both halogenated andotherwise, from air at room temperature, and then acts as a catalyst athigher temperatures (350° C.) to both desorb and oxidize trapped VOCs.Due to their microporous crystalline structure, various forms ofzeolites like zeolite A (3A, 4A and 5A), Faujasites (zeolites X and Y)and Pentasils (ZSM-5 and Silicalite) have been widely used as commercialadsorbents. Two dual function media, Cr-Y and Cr-ZSM-5 as well asmetal-loaded Co-Y zeolite catalyst, prepared by Greene, Prakash andAthota (J. of Applied Catalysis B: Environmental 7 (1996) 213-224), andRamachandran, Greene and Chatteijee (J. of Applied Catalvsis B:Environmental 8 (1996) 157-182), are given below and included here byreference in their entirety.

[0047] Cr-Y is made by exchanging NH₄—Y with chromium nitrate solutioncontaining 1.5 gram of chromium nitrate in one liter of distilled watermaintained at a pH of 4 for 72 hours. NH₄—Y is prepared by exchanging15-20 grams of H—Y (LZ-Y-84 from UOP, Si/Al=2.5, 20 wt % alumina asbinder) with 2.24 mol/l ammonium chloride solution for 2 hours. Cr-ZSM-5is made by exchanging NH₄-ZSM-5 with chromium nitrate solutioncontaining 2.3 grams of chromium nitrate in one liter of distilled waterat 50° C. for 72 hours. NH₄-ZSM-5 is prepared by exchanging 15-20 gramsof H-ZSM-5 (MFI from UOP, Si/Al=16, 20 wt % alumina as binder) with 2.24mol/l ammonium chloride solution. After repeated washing, both exchangedcatalysts are dried and subsequently calcined at 500° C. Typicalexchanged chromium loading of the Cr-Y and Cr-ZSM-5 catalysts were 0.6and 0.3 wt %. Typical BET surface area of the Cr—Y and Cr-ZSM-5 dualfunction catalysts were 474 and 388 m²/g.

[0048] To prepare Co—Y, about 20 grams of NH₄—Y is cobalt exchanged witha solution containing 16 grams of Co(NO₃)₂.6H₂O dissolved in 1 l ofdeionized water. The solution is stirred continuously for 48 hours at90° C. Typical cobalt loading on the zeolite was 1.5 wt %. After theexchange of all the cobalt ions in the cobalt nitrate solution with H⁺ions of the zeolite catalyst, the pellets were thoroughly washed withdeionized water, dried at 120° C. for 2 hours and then calcined at 500°C. for 10 hours. The measured BET surface area of the Co—Y catalystexceeds 600 m²/g of catalyst.

[0049] Still another media useful for the practice of this invention hasbeen disclosed by U.S. Pat. No. 5,720,93 1 to Rossin for catalyticoxidation of organic nitrogen-containing compounds. Typical catalystcomposition comprises a noble or a base metal supported on titania(Degussa P-25^(R)) or zirconia with added promoters such as molybdenum,tungsten, or vanadium. A typical formulation given by EXAMPLE I of theU.S. Pat. No. 5,720,931 is incorporated hereby reference, in itsentirety. 25 g of Degussa P-25 titania powder is slurried in 250 mldeionized water. To the slurry is added 2.9 g of lanthanum nitratehydrate dissolved in 30 ml distilled water. The slurry is placed in arotary evaporator at 45° C. Water is evaporated from the slurryovernight. The remaining solid is dried at 125° C. for 2 hours. thencrushed and sieved to 25/60 mesh granules. The granules are thencalcined at 450° C., for four hours. Approximately 8 g of this granulesare slurried in 200 ml distilled and deionized water. To this slurry isadded approximately 0.9 g ammonium metavanadate dissolved in 80 mldistilled and deionized water. The slurry is then placed in a rotaryevaporator at 60 ° C. and water is completely evaporated. The remainingsolids are then dried at 125 ° C., for two hours, then calcined at 450 °C., for four hours. About 2 g of the resulting granules is slurried in50 ml deionized water. Then, 0.04 g tetraamnine-platinum nitratedissolved in 25 ml distilled, deionized water is added to the slurry.The slurry is placed in a rotary evaporator at 60 ° C., and the water isevaporated overnight. The resulting material is dried at 125 ° C., fortwo hours, then reduced in a hydrogen atmosphere for another two hours,at 450° C., then calcined at 450° C., for two hours. The resulting finalproduct contains approximately 1-wt % Pt, 5-wt % V, 5-wt % La, andremaining TiO₂ support.

[0050] A further description of photocatalytic patents will now bedescribed:

[0051] U.S. Pat. No. 5,790,934 to Say et al. discloses a compact reactorfor the photocatalyzed conversion of contaminants in a fluid stream Thereactor includes a support structure with multiple non-intersectingaluminum fins oriented parallel to the general flow direction of thestream. The fins were spray coated with a 1:1 mixture of titaniumdioxide photocatalyst and alumina. Several germicidal lamps wereinserted into the fins that totaled 148 pieces that were either flat orpleated. The photocatalytic reactor of Say et al. had severalalternative designs but all included a large number of flat or pleatedfins or baffles at various relative configuration to the light source.Although, it is understood that such a design does present certainadvantages with respect to the contaminants mass transfer to thephotocatalytic surfaces, it is not at all clear how such configurationscan be useful in insuring a uniform radiance over all catalytic surfacesat or near q_(EK). Furthermore, no effort was made to decouple theprocess energy efficiency from the DRE of the target pollutant(formaldehyde vapor). Also, no references are given to the use ofmultifunctional photo and thermocatalytic media of the Type III-Vconfiguration.

[0052] U.S. Pat. Nos. 4,888,101 & 5,116,582 to Cooper and U.S. Pat. No.5,736,055 to Cooper et al. disclose several titania-based substantiallyof the Type 0 slurry photoreactor designs. In one application, areplaceable cartridge for use in a photocatalytic fluid purification isdescribed. The fluid flows through the cartridge in the presence oflight. The cartridge includes a flexible; porous element having titaniacoating associated with it and a rigid support structure. In anotherembodiment of the invention, a system for photocatalytic modification ofa chemical composition comprising substantially titania entrapped withina layer of Pyrex glass wool interposed between two transparent plates.In yet another embodiment, a photocatalytic slurry reactor is disclosedthat is driven by solar or artificial UV illumination. A tubular UV lampis suspended by an O-ring within a cylindrical reactor jacket, creatingan annular region through which a titania slurry is pumped. A helicalstainless steel wire wrapped about the bulb acts as a turbulencegenerator to break up the boundary layer for increased radial mixing.

[0053] These processes are substantially Type 0 slurry reactors withgenerally acceptable mass transfer characteristics but nonuniformirradiance over catalytic surfaces. i.e. category I limitation. Noeffort was made by these researchers to decouple the process energyefficiency from DRE of the target pollutants. Also, no references aregiven to the use of multifunctional photo/thermocatalytic media of theType III-V configuration.

[0054] U.S. Pat. Nos. 5,604,339 & 5,744,407 to Tabatabaie-Raissi et al.describe the use of photocatalysts, and in particular titania as coatingon the woody or biopolymeric support materials as an in-situ treatmenttechnique to prevent emission of harmful volatile organic compounds suchas formaldehyde, α-pinene, β-pinene and limonene from emitting surfaces.This invention is strictly an in-situ application and no description ismade of ex-situ treatment of airborne contaminants or process vent gasesutilizing a photoreactor. No references are given to the use ofmultifunctional photo/thermocatalytic media of the Type III-Vconfiguration or the use of decoupled media and processes similar tothose disclosed here.

[0055] U.S. Pat. No. 5,638,589 to de Lasa et al. as previouslyreferenced describes a photocatalytic reactor that requires fiberglassmesh supported photocatalyst wherein only polluted water passes throughand treated. The fiberglass mesh is substantially inorganic compound andnot a carbon containing synthetic polymeric or biopolymeric materialthat enhances destruction of pollutants. de Lasa et al. describe noseparate series connection of different reactors, nor parallelconnections of the reactors, nor different length of catalytic media.Furthermore, the conical baskets do not allow for maximum or uniformcollection and distribution of the light source photons. Finally, deLasa et al. has no teaching for thermocatalytic or combined thermo- andphotocatalytic media and reactor applications. There are no referencesto decoupling phenomena and means to mitigate that effect in U.S. Pat.No. 5,638.589.

[0056] U.S. Pat. No. 5,580,461 to Cairns et al. teaches a process fortreating a fluid comprising at least one chemical contaminant. Theirpurification process involves first contacting the contaminated fluidwith a particulate adsorbent material to adsorb the target compound. Thecontaminant-loaded adsorbent is then separated from the fluid andbrought into contact with aqueous slurry of a suitable photocatalyst.The contaminant on the adsorbent material is decomposed to form aproduct. The product of photocatalytic decomposition is then removedfrom the adsorbent material and slurry solution. The regeneratedadsorbent material and photocatalyst slurry is recycled. Themacro-process described by Cairns et al. employs a combined Type 0process, does not teach a photoreactor design and the approach issubstantially different from the reactors/processes disclosed here.There are no references made to decoupling.

[0057] U.S. Pat. No. 5,564,065 to Fleck et al. teaches a reactionchamber which is filled with a fine fibrous material capable of holdingpowdered titania. At the center of the chamber is a source ofultraviolet light. Air contatinig carbon monoxide is passed through thereaction chamber to be oxidized into carbon dioxide, which then removedout of the filter. An alternative embodiment uses a rectangular plateseveral feet square containing fibrous material and TiO₂. The reactordesign for this application is similar to that of U.S. Pat. No.5,126,111 to Al-Ekabi et al. The process is substantially a Type I mediaapplication with the Category I radiation field. No description is givenregarding the use of multifunctional photo and thermocatalytic mediahaving Class III-V configuration. No references are given to thecoupling phenomena or methods to deal with that effect.

[0058] U.S. Pat. No. 5,374,405 to Firnberg et al. teaches a rotatingfluidized bed reactor in which inert solid particles are held in placeby centrifugal force. The reactor includes a rotating porous bed drumwithin a plenum vessel. Gas enters through the walls of the drum andexits at the top. An ultraviolet light source is included within thedrum for effecting photochemical reactions. In one embodiment, the solidparticles are inert and loaded with reactant, which react with the gas.In other embodiments of this disclosure, the particles do not containthe reactant and reactant is provided within the gas stream. Noreferences are given to the use of medium-pressure mercury lamp inconjunction with the multifunctional photo/thermocatalytic media of theType II and V. No description of the decoupling of process energyefficiency from contaminants DRE is given. No direct reference to theuse of bandgap semiconductor photocatalysts such as titania or use ofhigh-power lamps are disclosed.

[0059] U.S. Pat. No. 5,246,737 to Muradov teaches a method forimmobilizing a semiconductor or noble metal material on a number ofsupports including biopolymers. A solution containing methylene chlorideand silicone polymer mixed with titania catalyst was used to formslurry. The slurry was applied onto the surface of cotton fiber with asoft brush. No description is given for treating airborne contaminants.Moreover, Muradov does not teach a process or photoreactor to accomplishvapor-phase detoxification. Also, the application of photocatalyst insolution with a solvent containing silicone can adversely affectphotocatalyst activity toward oxidative mineralization of environmentalpollutants. No references are made to the use of multifunctional photo-and thermocatalytic media of the Type III-V configuration. Also, thereis no mention of the use of decoupled media or processes similar tothose disclosed here.

[0060] U.S. Pat. Nos. 4,966,759, 4,892,712 & 5,032,241 to Robertson etal. and U.S. Pat. No. 5,126,111 to Al-Ekabi et al. describe methods forimmobilizing TiO₂ and other photoactive compounds onto a porous,filamentous, fibrous/stranded glassy transparent mesh for ex-situoxidation and removal of organic pollutants from fluids. Like U.S. Pat.No. 5,035,784 to Anderson, these are also based on Type IIphotocatalyst/support and photo-processes. The mesh/matrix can befiberglass material that supports the sol-gel deposited titaniaphotocatalyst. Robertson et al. correctly recognized usefulness ofdispersing the photocatalyst uniformly throughout the reaction volume inmuch the same way titania slurry is prepared. They also recognized thatin a practical slurry-free process, TiO₂ must be immobilized onto asuitable transparent support to allow UV transmission and uniformcatalyst illumination. The manner in which fiberglass-supported titaniais meshed and wrapped around the UV lamp does not produce a well-definedcatalytic media that is reproducible and permit uniform catalyst surfaceirradiance. It is abundantly clear from the previous discussions that aglassy mesh type photocatalytic matrix/media does not readily allow foruniform surface irradiance like the Category I media and photoreactordesign. Also, Robertson et al. and Al-Ekabi et al. provide no referencesto the use of multifunctional photo- and thermocatalytic media withClass III-V configuration and no references are made to decoupledreactor/process designs disclosed here.

[0061] U.S. Pat. No. 5,069,885 to Ritchie teaches an apparatus forpurification of water in a tubular photoreactor that includes anon-transparent substrate coiled longitudinally and helically around atransparent sleeve. The non-transparent substrate has photocatalystmedia bonded to it. Like U.S. Pat. No. 5,035,784 to Anderson, this isalso Type II media, Category I radiation field. No references are givento multifunctional photo- and thermocatalytic media of Class III-Vconfigurations. No description of the coupling phenomena and methods tomitigate that are given or discussed.

[0062] U.S. Pat. No. 5,045,288 to Raupp et al. describes a technique forremoving halogenated volatile and nonvolatile organic contaminants froma gaseous stream by mixing with a gaseous oxygen bearing substance inthe presence of a solid metal oxide catalyst exposed to near ultraviolet(UV) radiation. This patent has a Type I photocatalyst/supportconfiguration. Raupp et al. does not teach a photoreactor design ormention polyfunctional catalysts like those disclosed here. Noreferences to the coupling phenomena and methods to mitigate that aregiven.

[0063] U.S. Pat. No. 5,035,784 to Anderson et al. teaches a method forthe degradation of complex organic molecules, such as polychlorinatedbiphenyls on porous titanium ceramic membranes by photocatalysis underultraviolet light. A special membrane preparation technique known as“sol-gel” process is used. An organometallic titanium compound ishydrolyzed to form a soluble intermediate, which then condenses into theorganic titanium polymer. The process includes the preparation of aparticulate gel, which is fired to achieve a ceramic material. Andersonet al. note that the control of process parameters is crucial, oneimportant factor being the sintering temperatures at or below 500° C. togive a hard dry ceramic. It is not possible, nor desirable todeposit/immobilize ceramic like membranes atop surfaces of polymeric,biopolymeric (e.g. wood, paper, etc.) origin subject to the very highsol-gel preparation temperatures that will undoubtedly destroy thesubstrate. The photocatalyst/support arrangement is substantially TypeII configuration. The patent by Anderson et al. does not teach aphotoreactor design or mention the use of multifunctional catalystssimilar to those disclosed here. No references are made to the couplingphenomena and techniques to mitigate that.

[0064] U.S. Pat. No. 4,966,665 to Ibusuki et al. describes anapplication involving vapor-phase, TiO₂-based photocatalysis of processvent gases containing chlorinated VOCs such as trichloroethylene (TCE)and tetrachloroethylene, is substantially a Type I photocatalyst/supportapplication. No references are made to the use of multifunctional mediahaving Type III-V configuration or the decoupled reactor designs similarto those disclosed here.

[0065] U.S. Pat. No. 4,446,236 to Clyde teaches a photochemical reactorwhich is divided into a first section suitable for containing a volumeof fluid and a second section having at least one light transmittingwall. A porous, high surface area, fiber webbing is mounted within thereactor so that a portion of the webbing is immersed in the fluid to bereacted. The webbing moves within the reactor so that the webbing issequentially immersed in the fluid contained in the first reactorsection and then moved to the second reactor section where the webbingand fluid therein are irradiated. This process is substantially a Type 0application and Category I radiation field design. Furthermore, noreference is given to mitigating the coupling effect present.

[0066] U.S. Pat. No. 3,781,194 to Juillet et al. teaches an applicationinvolving vapor-phase photocatalysis using TiO₂ in a manner similar tothe U.S. Pat. No. 5,045,288 by Raupp et al. The only difference betweenthis patent and the one described above is that Juillet et al. teach amethod for oxidizing hydrocarbons to produce aldehydes and ketones,while, Raupp and Dibble describe a similar method for oxidizinghalogenated organic compounds such as TCE.

SUMMARY OF THE INVENTION

[0067] A primary object of the invention is to provide a photoprocessand apparatus for an energy efficient mineralization and detoxificationof organic pollutants or undesirable chemicals in both gaseous andaqueous streams.

[0068] A secondary object of this invention is to provide apparatus andteach methods of treating contaminated fluids using catalysts and energysources capable of exciting and activating those catalysts. The energysources capable of exciting and activating the catalysts include, amongothers, mercury vapor lamps (low, medium and high pressure, blacklightand fluorescent light and actinic), xenon lamps (including xenon-mercuryand xenon flashlamp) and halogen lamps. In general, these light sourcesfall into two distinct classes, namely, low and high-power lamps. Thecatalyst can be a unifunctional, multifunctional or combination ofseveral unifunctional catalysts. Chemical composition, materials ofchoice and physical configuration of the catalyst is so chosen to becompatible with the choice of the light source and allow its efficientimplementation in the decoupled reactors (full and partial) andtreatment processes of the present invention. Both low-flux andhigh-flux media and reactors are based on well-developed principles thatinclude:

[0069] (i) Fluid passage with no mass transfer intrusions.

[0070] (ii) Uniform radiance over all catalytically active surfacelayers.

[0071] (iii) Decoupled process energy efficiency from the DRE of targetcontaminants.

[0072] (iv) Utilization of both photons and process waste heat by usingmultifunctional media.

[0073] (v) Simple and readily scaleable photoreactor/photoprocessdesign.

[0074] A third object of the invention is to provide an energy efficientphotoprocess and apparatus wherein the catalyst is bonded to the fabricof the base material (i.e. flexible stocking or rigid, metallic orceramic screen).

[0075] A fourth object of this invention is to construct a flexible basematerial, hereafter called “stocking” substantially from a naturalpolymeric (biopolyrneric), synthetic polymeric or a combination of bothnatural and synthetic polymeric material to which a suitablephotocatalyst is firmly applied. It is another object of this inventionto expose the catalytic stocking to radiation in the range ofwavelengths from 184 to 400 nanometers.

[0076] A fifth object of the invention is to fabricate the rigidmetallic base material, hereafter called “support” substantially fromany suitable metal, metal oxide or an alloy such as 316 or 304 stainlesssteel.

[0077] A sixth object of this invention is to surround the light sourcewith either stocking or the support on to which a suitablephotocatalytic, thermocatalytic or a combination of photo- andthermocatalytic material has been deposited, called hereafter “low-fluxcatalytic media.”

[0078] A seventh object of the invention is to allow the contaminantstream to pass through the low-flux media, substantially in lateraldirection, in a manner that permits retention of the target specieswithin the low-flux catalytic media in a most efficient manner.

[0079] An eighth object of the invention is to promote fullmineralization of the primary (target species) and secondary reactantsto innocuous final products. The plurality of a light source radiatingat the above-mentioned wavelength range and the low-flux catalytic mediasurrounding the light source, axisymetrically, is referred to hereafter“single photocell arrangement”.

[0080] A ninth object of the invention is to provide a flow regimethrough the singe photocell arrangement that minimizes mass transferintrusions to the low-flux media.

[0081] A tenth object of this invention is to provide an optimumconfiguration that allows most efficient radiant exchange from the lightsource to the low-flux media and most uniform catalyst surfaceirradiance.

[0082] An eleventh object of the present invention is to provide asegmented low-flux catalytic media; hereafter referred to as “low-fluxmulti-stage media” that allows multiple passage of the contaminatedstream through the low-flux photocatalytic, thermocatalytic or combinedphoto- and thermocatalytic media.

[0083] A twelfth object of the invention is to segment the low-fluxphotocatalytic media in a single photocell arrangement in a manner thateither maximizes the quantum efficiency of the photoprocess or minimizesthe pressure drop across the single photocell, i.e., the differencebetween the pressures measured at exit port and inlet port of the singlephotocell unit.

[0084] A thirteenth object of the present invention is to provide anovel gas-solid contacting scheme and photoreactor (photocell) designthat is most suited for use with the single-stage and multi-stage,low-flux media based on the bandgap photocatalysts, i.e. single-stageand multi-stage photocatalytic media.

[0085] A fourteenth object of this invention is to arrange several ofthese photocatalyic media, in parallel together, each with its owndedicated ultraviolet light source within an integrated reaction vessel,hereafter called “photocatalytic bank”.

[0086] A fifteenth object of the invention is to connect/plumb togethera number of banks in series to form a “photocatalytic module”.

[0087] A sixteenth object of this invention is to connect/plumb togethera number of photocatalytic modules, in parallel or in series, to form aphotocatalytic pollution control “unit” or PPCU.

[0088] A seventeenth object of the invention is to arrange and plumb thesub-units of the PPCU in such a manner that either maximizes the overallenergy efficiency (apparent quantum efficiency or photoefficiency) ofthe photocatalytic unit or minimizes the pressure drop across thephotocatalytic unit (i.e. the difference between the exit port and inletport pressure).

[0089] The subject inventor has determined in the subject invention if alinear light source (e.g. a low- or medium-pressure mercury vapor lamp)is used, then the best catalytic media arrangement will be one having acylindrical (tubular) configuration. Within that configuration, the UVlamp is placed most advantageously along the media axis. It is alsodesirable to minimize the number of light blocking internals such asbaffles, fins, turbulators, pleats, ribs, etc. As such, the activesurface of the catalytic media would receive the most uniformirradiance. In the case of high power lamps such as medium- andhigh-pressure mercury vapor lamps, the type and configuration of thephotocatalyst/support (media) is even more critical. This is so becausethe high power lamps emit radiation and heat at a level orders ofmagnitude higher than the low-pressure mercury lamps (LPMLs). The outputpower of a typical commercial LPML is approximately 1 W/in. On the otherhand, medium-pressure mercury lamps (MPMLs) are commercially availablewith power output of up to 300 W/in, nominal. For the irradiance at thephotocatalyst surface to remain at or near q_(EK), a minimum distance,l_(EK), between the light source and the catalyst surface must bemaintained. l_(EK) is a design parameter and characteristic of the typeof UV light source used in the photoreactor. In the case of a tubularcatalytic media irradiated with a single low-, or medium-pressuremercury lamp, l_(EK) is calculated to be approximately 3.8 inches and 68feet, respectively. For calculating l_(EK), the electric to UV lightenergy conversion efficiency of 0.3 and 0.15 has been assumed forstandard LPML and MPML (300 W/in), respectively.

[0090] Clearly, based on the l_(EK) calculations determined by thesubject inventor, the implementation of LPMLs as the source of UVradiation in practical photoreactors should not be unusually difficultas long as provisions are made to ensure uniform irradiance over allcatalytic surfaces. In other words, LPML-driven systems are generallysimpler to design and can accommodate many different types of media andreactor configurations. Thus, the primary consideration in constructingan LPML-based photoprocess is to engineer a uniform radiance over allcatalytic surfaces and design for maximum energy efficiency. Theessential feature of such an energy efficient photosystem design isdecoupling of the process photo-efficiency from conversion efficiency(or DRE) of the target contaminants. Accordingly, it is an object ofthis invention to provide a novel and improved LPML-based photocatalyticmedia (hereafter called “low-flux media”) and a photosystem design thatis highly energy efficient. The novel features of such a design will bedisclosed later in this document.

[0091] Unlike, LPML-driven photoprocesses, MPML-based systems, asindicated by the l_(EK) calculation, require large and unrealisticphotoreactor dimensions to accommodate both the photocatalyst and thelight source. The requirements of very large catalyst surface areaoptimum surface irradiance, uniformity of light distribution and mediathermal management in MPML-based photo-processes pose a real designchallenge. Therefore, it is clear that most photocatalyst/supportmaterials and media configurations of the prior art are not particularlyuseful for the MPML-based photoreactors. Thus, another object of thepresent invention is to provide a new and novel method and process forimplementing high power light sources for photo and thermocatalyticservice that is compact and highly energy efficient The approach isbased on the use of transition metal aerogel supported catalytic mediaand others within a specially designed photoreactor. In the terminologyof the present application, MPML-based processes and media hereaftertermed as the “high-flux” processes and media.

[0092] For high-flux applications, a rotating fluidized bed photoreactoris most desirable. The photocatalytic media is in the form ofmultifuntional, moderate temperature catalysts of the Type III (e.g.metal oxide aerogels, co-gelled metal oxide aerogels includingtitania-silica aerogels and transition metal aerogel-supportedcatalysts, etc.) or Type V (e.g. supported transition metal oxidecatalysts, cation modified zeolites and doped titania catalyst). Thereactor consists of a porous rotating drum located within a stationaryplenum vessel. The waste stream enters the rotating drum through theporous side wall of the drum and exits from an opening near the top.Rate of the rotation of the drum and amount of solids added and bedthickness is adjusted to minimize bed carry over and maintain operationat or near minimum fluidization condition wherein the bed materialexpands but few bubbles are formed within the bed. A medium pressuremercury lamp placed within a quartz or fused silica sleeve at the middleand inserted into the photoreactor from the bottom or top. Provisionsare made to allow feeding and removal of the photocatalytic media duringnormal reactor operation, if necessary.

[0093] Therefore, other objects of the invention described here are toprovide gas-phase photocatalysis and air purification system with veryhigh process quantum efficiency for treating various organiccontaminants including: aliphatics, aromatics, halogenated organics,mercaptants, sulfur gases, and others.

[0094] Further objects and advantages of this invention will be apparentfrom the following detailed description of the preferred embodiments,which are illustrated schematically in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0095]FIG. 1a shows a photocatalyst-coated monolith, a Category I designof the prior art.

[0096]FIG. 1b depicts photocatalyst-coated panels, a Category I designof the prior art.

[0097]FIG. 1c displays a photocatalyst-coated baffled annularphotoreactor, a Category I design of the prior art.

[0098]FIG. 2 shows the variation of wall irradiance for photocatalyticdesign of prior art depicted in FIG. 1c for the case in whichphotocatalyst surface emissivity is unity (i.e. all UV radiationincident on photocatalyst is absorbed), k=D_(l)/D₀=0.375, D_(i)=25 mm,and 65 W LPML.

[0099]FIG. 3 is the experimental set up for surface irradiancemeasurements in a clustered tri-lamp photoreactor.

[0100]FIG. 4a and 4 b depict lateral variation of wall irradiance intri-lamp annular baffled photoreactor. Normalized wall irradiance isgiven at mid-point between two neighboring baffles for a three lampcluster (8 W each), lamp radius of r_(lamp)=0.31″ and single lamp wallpeak irradiance of q_(l,∞)=3.69 mW/cm², and packing ratio of a)r_(p)/r₀=0.333 and b) r_(p)/r₀=0.452.

[0101]FIG. 5 shows lateral variation of wall radiance in tri-lampannular baffled photoreactor with refraction effects. Normalized wallirradiance is given at mid-point between two neighboring baffles for athree lamp cluster (8 W each), lamp radius of r_(lamp)=0.31″ and singlelamp wall peak irradiance of q_(l,∞)=3.69 mW/cm², and packing ratio ofr_(p)/r₀=0.333.

[0102]FIG. 6 depicts the scheme of hydrogen bonding of titania tocellulose polymer.

[0103]FIG. 7a shows the scanning electron micrograph of Kemira UNITI908^(R) catalyst particles on cotton (flannel) fibers, according to thesubject invention.

[0104]FIG. 7b shows the scanning electron micrograph of Kemira UNITI908^(R) catalyst particles dispersed on a fiberglass mesh support (PRIORART).

[0105]FIG. 7c shows the scanning electron microraph of TiO₂ catalyst onfiberglass mesh prepared by the sol-gel technique of U.S. Pat. No.4,892,712 to Robertson et al. (PRIOR ART).

[0106]FIG. 8a depicts the air flow and surface irradiance distributionpattern over and within cotton (flannel) fabric fibers coated with TiO₂according to the subject invention.

[0107]FIG. 8b depicts the air flow and surface irradiance distributionpattern over and within fiberglass mesh supported titania in the priorart.

[0108]FIG. 9a shows a schematic diagram of a single-stage, low-fluxreactor configuration of the subject invention depicting flow of thecontaminated stream through the photocatalytic stocking.

[0109]FIG. 9b shows a schematic diagram of a single-stage, high-fluxreactor configuration of the subject invention depicting flow of thecontaminated stream through the rotating bed of fluidized photocatalyticparticles.

[0110]FIG. 10 depicts photocatalytic oxidation of ethanol in a 1 gfluidized bed reactor and a small gap annular flow reactor.

[0111]FIG. 11a is a schematic diagram of the single-cell photoreactorapplication of the subject invention having a single-stage low fluxcatalytic media (stocking).

[0112]FIG. 11b is a schematic diagram of the experimental setup forlow-flux flow photoreactor tests of the subject invention.

[0113]FIG. 12 shows experimental flow reactor data for nitroglycerineconversion, obtained in a single photocell equipped with a single-stagecotton stocking of 60 inches long and different diameters. A 60″ longlow-pressure mercury lamp (Voltarc^(R) T64T6) having 65 W nominal poweris used.

[0114]FIG. 13a depicts the schematic diagram of a single-cellmulti-stage (of unequal lengths) low-flux catalytic reactor of thesubject invention for decoupling calculations.

[0115]FIG. 13b shows a flow chart for determining optimum partitioningratios of FIG. 13a.

[0116]FIG. 14a shows the schematic diagram of a single-cellequipartitioned (all segments of equal length) low-flux catalyticreactor of the subject invention for decoupling calculations.

[0117]FIG. 14b shows a flow chart for determining performance ofsingle-cell equipartitioned multi-stage catalytic reactors of thesubject invention.

[0118]FIG. 14c shows the schematic diagram of a single-cellequipartitioned (all segments of equal length) high-flux centrifugalfluidized bed catalytic reactor of the subject invention for thedecoupling calculations.

[0119]FIG. 15 depicts the performance of a single-cell multi-stageequipartitioned (all segments of equal length) catalytic media;Voltarc^(R) Model T64T6-VH low-pressure mercury lamp, 60 inches long and65 W nominal power, flannel cotton fabric as the base material withpermeability of 0.075″H₂O/cps (typical), inlet nitroglycerin (NG)concentration of 10 ppmv, required NG destruction and removal efficiency(DRE) of 99.5%.

[0120]FIG. 16 depicts one embodiment of a low-flux, double-stagephotocatalytic stocking of the present invention.

[0121]FIG. 17 shows one embodiment of a low-flux, triple-stagephotocatalytic stocking of the present invention.

[0122]FIG. 18 depicts experimental vs. predicted performance forlow-flux, multi-stage photocatalytic reactors of the present invention.

[0123]FIG. 19a depicts the schematic diagram of two multi-stageequipartitioned (all segments of equal length) low-flux series catalyticreactors of the subject invention for decoupling calculations.

[0124]FIG. 19b shows a flow chart for determining performance ofsingle-cell equipartitioned multi-stage catalytic reactors of thesubject invention.

[0125]FIG. 19c depicts the schematic diagram of two multi-stage (ofunequal lengths) low-flux series catalytic reactors of the subjectinvention for decoupling calculations.

[0126]FIG. 20 depicts the performance of a full-scale photocatalyticpollution control unit (PPCU) of the present invention, having twoparallel modules each employing two banks in series and segmented(multi-stage) cotton (flannel) stockings, for inlet concentration ofnitroglycerin C_(A0)=10 ppmv, 4″ OD photocatalytic stockings, and 60″long LPML (Voltarc^(R) T64T6-VH) 65 W nominal power.

[0127]FIG. 21a depicts the schematic diagram of a two-by-twoseries-parallel multi-stage equipartitioned (all segments of equallength) low-flux catalytic reactor of the subject invention fordecoupling calculations.

[0128]FIG. 21b depicts the schematic diagram of a two-by-twoseries-parallel multi-stage (of unequal lengths) low-flux catalyticreactors of the subject invention for decoupling calculations.

[0129]FIG. 22 depicts one embodiment of the present invention'shigh-flux media and photocatalytic reactor design.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0130] Before explaining the disclosed embodiments of the presentinvention in detail it is to be understood that the invention is notlimited in its application to the details of the particular arrangementsshown since the invention is capable of other embodiments. Also, theterminology used herein is for the purpose of description and not oflimitation.

[0131] The present invention provides a new process for catalytictreatment of contaminants in fluids that is energy efficient, andreadily scalable. The process employs catalytic media and an innovativefluid-solid contacting scheme. The performance enhancement is bydecoupling of the process energy efficiency from the DRE for targetcontaminants. The novel features, and specifics of this technique arebest demonstrated by an analytical treatise disclosed below. Themethodology is for the case of a low-flux photoprocess usingphotocatalytic media described before. The technique can be used in alike manner to analyze high-flux photoprocess and media of the present.

LOW-FLUX PHOTOCATALYTIC MEDIA OF THE PRESENT INVENTION

[0132] As far as the low-flux applications are concerned, the best mediatype and configuration is one that provides the most uniform loading ofthe undisturbed catalyst onto the base material/support while preservingthe optimum catalytic activity. It is to be understood that in theterminology of this disclosure, the low-flux catalytic media of thepresent invention include photocatalysts and base materials (supports)that operate at or below the process temperature of approximately 100°C. In the preferred embodiment of this invention, the catalyticmaterials include special multifunctional photocatalysts. Yet, inanother preferred embodiment of this invention, the base material is anintegral part of or a component of the catalyst material, collectivelycomprising the low-flux catalytic media. Furthermore, in yet anotherpreferred embodiment of this invention, the catalytic media suitable foruse with the low-power UV light source include woven polymeric materialsof natural origin (or biopolymers) such as cotton fabric and mostdesirably flannel cloth. Since cotton fibers contain a very highcellulose content, the chemical properties are essentially that of thecellulose biopolymer. Cellulose is a long linear polymer ofanhydroglucose units (C₆H₁₀O₅)_(n) and 1500<n<6000. The polymer unitsare organized into a thread-like structure (elementary fibrils of verylong length and approximately 3.5 nm in width). The elementary fibrilsare bonded laterally to provide further strength (microfibrils ofapproximately 10-30 nm long). Each anhydroglucose ring consists of threehydroxyl and two oxygen (—O—) moieties (ring and bridge). Thus, it ispossible for the TiO₂ molecules to bind to cotton fibers via followinghydrogen bonding (see FIG. 6):

[0133] (i) ˜Ti═OH—O—CH₂˜

[0134] (ii) ˜Ti—O—HO<(anhydroglucose ring); by hydroxylated TiO₂surface.

[0135] This may explain the superior catalyst adhesion to biopolymerfibers and the high degree of catalyst coverage and coating uniformityachieved.

[0136] The subject inventor has determined in the subject invention thatunaltered natural polymers such as woven cotton cloth and flannelprovide an excellent base material/support for bandgap photocatalysts.Biopolymeric materials are superior to other widely used media thatinclude ceramic and woven glass mesh type matrices of the prior art. Thelow-temperature catalytic media of the present invention, including theintegrated titania/biopolymer material, display low pressure drop,excellent stability and contaminant retention. FIG. 7 depicts thescanning electron micrographs of three catalytic media prepared at thesubject inventor's laboratory. FIG. 7a shows the Kemira Uniti 908^(R)titania immobilized onto a woven cotton cloth, as in the practice of thepresent invention. FIG. 7b depicts a fiberglass mesh support FIG. 7cshows titania deposited by sol-gel technique onto a fiberglass mesh (asin U.S. Pat. No. 4,892,712 by Robertson et al.). Modifications a, b andc are representative of the photocatalyst/support configurationsdesignated as Type IV, Type I and Type II, respectively. The uniformityand quality of catalyst deposition and dispersion on the woven cottoncloth (flannel) is readily observed. An explanation for the superiorperformance of the low-flux media of the present invention is givenbelow.

[0137]FIG. 8a depicts one preferred embodiment of the low-flux media ofthe present invention comprising TiO₂ particles within the cotton fibersas a Type IV media. FIG. 8a and 8 b show the likely pattern of fluidflow and light distribution within and around the media of the presentinvention and glass fibers (media Types I and II of the prior art),respectively. The uniform distribution of the catalyst particles oncotton fibers and relatively large distance between the fibersthemselves result in uniform flow and surface irradiance that issuperior to that obtained by catalytic media of the prior art (Type I &II). Furthermore, in the Type I and II media:

[0138] (i) Poor catalyst deposition allows bottom layers of thephotocatalyst unexposed to UV light and, hence, not participating in thereactions.

[0139] (ii) Non-uniform catalyst coating leads to irregular flow patternthrough the mesh.

[0140] EXAMPLES 1 to 3 describe the preferred embodiments of the presentinvention with respect to preparation of the low-flux media. It isimportant to note that the following examples detail the best methodsknown to the applicant at the time of filing this application. It isenvisioned that better techniques for the operation and preparation ofthe catalysts may be developed subsequently and are to be considered asa part of this specification thereof insofar as they come within thescope of the claims.

EXAMPLE 1

[0141] This EXAMPLE describes the manner in which one preferredembodiment of the invention's low-flux base material/support wasprepared. A rectangular piece of unaltered cotton fabric was machinewashed in hot water using a small amount of liquid detergent (e.g.Proctor & Gamble's Tide™), followed by two cold rinses. Then,tumble-dried at 55° C., approximately. The entire process above wasrepeated for the second time. Fabric's post-wash, fully shrunkdimensions were about 95% of the original, as received dimensions. Therectangular piece of fabric was then sewn along the seam and at bothends into cuffs.

EXAMPLE 2

[0142] This EXAMPLE describes the manner in which one preferredembodiment of the invention's low-flux catalytic media was prepared. Thecatalyst in the form of titanium hydroxide, TiO₂ or combination oftitanium dioxide and titanium hydroxide was added to the syntheticpolymeric, biopolymeric or combination of synthetic polymeric andbiopolymeric fibers of the base material/support having a concentrationin the range of 1-15 percent by weight of the media (base material andcatalyst). The preferred form of the titanium containing catalystmaterial is in the form of commercial compounds marketed under the tradenames such as Kemira UNITI-980^(R), Degussa P-25^(R), HombikatUV100^(R), Bayer Bayertitan 5585^(R) and Ishihara ST^(R) series (e.g.ST-01, ST-11 & ST-31), to name just few.

[0143] In one preferred embodiment of the present invention, thecatalytic material constitutes titania particles that comprise thecrystalline form of anatase or rutile, preferably anatase having BETsurface area greater than 45 m²/g, preferably greater than 225 m²/g; andparticle size smaller than 0.1 microns, preferably less than 0.02microns.

[0144] The titanium dioxide particles are firmly bonded to the basematerial via Van der Waals interaction and hydrogen bonding involvinghydroxylated titania surface and OH-groups of the cellulosicanhydroglucose rings. The catalyst is then jet-impregnated into the basematerial (fabric support) from a pressurized aqueous catalyst slurrysolution. The slurry solution was prepared and applied to the fabric byfirst dry ball milling titania powder so that all particles pass throughU.S. sieve #60 mesh. Then, admixing 17 grams of catalyst for every 1000ml of distilled water, preferably, deionized water (Ohmic resistance of18.5 MΩ). After sonicating each 2 L batch of the catalyst slurrysolution for approximately one hour, about 50 liters of thoroughly mixedand sonicated catalyst slurry solution was emptied into a glass jarplaced upon a magnetic stirrer. Using a PTFE stirring bar, the slurrysolution was continuously and vigorously stirred.

[0145] The glass jar containing the slurry solution was then pressurizedwith nitrogen to about 5 psig. The slurry solution was jet injected,through a ¼ inch PTFE tubing and injector head, onto the inner face ofthe stocking of EXAMPLE 1. The prewashed (preferably, machine-washed atleast once before sewing and once after), fully shrunk bone dry, andfully stretched tubular cloth (stocking) was then pulled over a tubularpolvinylchloride (PVC) arm. The cloth covered PVC tube turned slowly asthe injector head sprayed the catalyst slurry onto and into the fabricalong the PVC arm. Afterwards, the excess fluid was pumped out bysqueezing the surface of the fabric, wringing and finally centrifugingfor a period of approximately 15 minutes. Then, catalytic stockings weremachine dried, eight at a time, at about 55° C. for approximately 30minutes until bone dry. The catalyst loading on the fabric wasdetermined by weighing fully dried stocking for quality assurance tofall within the range of 0.5 to 1.2 mg of catalyst per cm² of fabricsurface area. Finally, to provide means for mounting the catalyticstocking within the photocatalytic unit, a Nylon® clamp (e.g. modelCX34, by Deflect-O Corp. or SUPERFLEX IN-LINE Nylon 6.6 model IT9115-COby Panduit Corp.) was inserted into each cuff.

EXAMPLE 3

[0146] This EXAMPLE describes the manner in which other preferredembodiments of the low-flux catalytic media were prepared. Differentorganic, inorganic and metal-organic additives were added to thecatalyst slurry of EXAMPLE 2. The solution containing the catalyst andadditive was then applied to the base material of EXAMPLE 1. Finally,the supporting base material (fabric) was allowed to dry overnight atroom temperature. The preparation method and other details for eachadditive is given in TABLE I. The rationale for using each additive isdisclosed below:

[0147] Acridine yellow dye (AY): As an organic dye performs two usefulfunctions: First, being a photocatalyst facilitates various electrontransfer reactions (e.g. photogeneration of hydrogen from aqueoussolutions of electron donors). Second, as a photosensitizer extends theabsorption properties of the base material/support ofsemiconductor-based photocatalysts. Acridine yellow is one of feworganic dyes that perform both functions. For example, prior art(Muradov, N. Z., et al. Reaction Kinetics and Catalysis Letters. v.3/4,1981, 355) teaches that AY is an effective photocatalyst for the visiblelight (450-500 nm) induced photoreduction of methylviologen (MV²⁺) inthe presence of organic donor EDTA with the quantum yield of 56%,according to (vi)

MV²⁺+EDTA+{hv/AY}→MV ⁻+EDTA_(ox)  (vi)

[0148] Another advantage of using AY as a co-catalyst and sensitizer forTiO₂ is its relatively high resistance to oxidation.

[0149] Fe(NO₃)₃: Prior art teaches that Fe³⁺ ion is a powerfulphoto-oxidant when exposed to near-UV radiation in aqueous solution,according to (vii)

Fe³⁺+D+hv(near UV)→Fe²⁺ +D _(ox)  (via)

[0150] Where, D and D_(ox) is the original and oxidized form of theorganic compound, respectively. OH-radicals can be produced from Fe³⁺ byeither light reaction with adsorbed water molecules, as in (viii):

Fe³⁺+(H₂O)_(ads) +hv→Fe²⁺+OH^(•)+H⁺  (viii)

[0151] or by intermediate H₂O₂ formed via dark reaction (ix):

Fe³⁺+(H₂O₂)_(ads)→Fe²⁺+OH^(•)+H⁺½O₂  (ix)

[0152] Partial hydrolysis of Fe(NO₃)₃ can form Fe₂O₃ that will remain onthe titania surface and as the prior art teaches (Ibusuki, T., and K.Takeuchi, J. Molecular Catalysis, 88, 1994, 93) can act as a co-catalystwith TiO₂ in various photo-oxidation processes (e.g. photo-oxidation ofNO₂ to HNO₃).

[0153] Platinum (Pt): The main function of Pt as a co-catalyst is itsability to mitigate electron transfer reactions by forming a reservoirfor electrons. Presence of Pt colloids on the titania surface canpotentially facilitate and prolong separation of the photogeneratedelectrons and holes thus increasing the overall efficiency of thephotoprocess. Also, Pt can catalyze the oxygen reduction process forproducing peroxoradicals as in (x):

O₂ +e ⁻+H⁺→HO₂ ^(•)  (x)

[0154] Peroxoradicals can be the source of additional hydroxyl radicals,the main active species in oxidative destruction of organics, thus (xi):

2HO₂ ^(•)→2OH^(•)+O₂  (xi)

[0155] Platinum can also catalyze undesirable reactions, for example,the termination of OH-radicals via formation and decomposition ofhydrogen peroxide according to the following reactions: (xii), (xiii),and (xiv)

2OH^(•)→H₂O₂  (xii)

OH^(•)+H₂O₂→H₂O+HO₂ ^(•)  (xiii)

2H₂O₂→H₂O+O₂  (xiv)

[0156] Activated carbon (AC): The rationale for using superactivatedcarbon (surface area 250 m²/g) as an additive to TiO₂ is to enhance themass-transfer characteristics of the catalyst/support structure byincreasing the surface area of the media. Apparently, once NG isadsorbed on the AC surface it diffuses to the titania surface thusincreasing NG local concentration and, thus, increasing the apparentquantum efficiency. However, it is very important to employ an optimumAC/TiO₂ ratio, because at high AC/TiO₂ ratios, AC is likely to adverselyaffect the system efficiency by depriving TiO₂ surface from usefulphotons.

[0157] NaOH: Prior art (Samodjai, G., in Photocatalysis: Fundamentalsand Applications N. Serpone and E. Pelizzetti (Editors), WileyInterscience, New York, 1989, 251) teaches that alkali hydroxides (KOHor NaOH) catalyze the hydroxylation of oxide semiconductors (e.g.SrTiO₃) surfaces and thus, facilitate certain photocatalytic processes(e.g. water dissociation). Since the rate of OH-radical photogenerationis a function of the concentration of surface hydroxyl groups, then itis plausible that hydroxylation of the titania surface can affectkinetics of photo-oxidation. TABLE I Volume Photocatalyst Additive ofslurry (g) (wt %) (ml) Preparation details DP (20.45) None 300 Slurry DP(5.74) None 750 Slurry DP (10.34) None 400 Slurry H-UV (10.50) None 400Slurry KU (10.50) None 350 Slurry SrTiO₃ (11.00) None 600 Slurry KU(12.01) None 700 As received dyed (red) fabric KU (12.00) AY (0.41) 500100 ppm by weight Acridine yellow solution KU (12.00) NaOH (45.83) 500Added 100 ml of 5.5 wt % NaOH solution KU (12.00) Fe(NO₃)₃ (16.67) 500Added 100 ml of 2 wt % of Fe(NO₃)₃ solution Pt/KU (12.00) Pt (1.82) 50046 ml of 1 wt % H₂PtCl₆ diluted in 100 ml of water, purged with H₂ at60° C. for 3 hrs KUXA (12.00) None 600 Slurry KUXA (12.00) AY (0.41) 500Added 100 ppm by weight Acridine yellow to solution KU (12.00) Saffron(1.50) 750 0.18 g of crushed Saffron in H₂O added to KU slurry DP (12.0)AC (15.00) 750 1.8 g of activated carbon AX-21 added to DP slurry

[0158] Finally, particular choice of the catalyst also depends on thespecific application involved. For example, when chlorinated compounds(e.g. trichloroethylene, TCE) are treated, hydrochloric, acid is oftenformed as one of the final products. The chloride ion bonds strongly tothe noble metals such as platinum and palladium when present incombination with Ti₂, SiO₂, or SiO₂ supported TiO₂. It has been observedthat the noble metal deactivates quickly under these conditions due tothe strong affinity of the chloride ions for noble metals.

[0159] Iron (Fe) as a transition metal can exist in two stable oxidationstates, ie. Fe²⁺ and Fe³⁺ and can catalyze reduction of halogenatedorganics. But, in a moist environment with excess oxygen iron oxideforms leading to the catalyst inactivation. However, in a combined metaland metal oxide-supported noble metal catalyst, the SiO₂ support of thehigh-flux media (or carbonaceous substrate of the low-flux media)adsorbs target species and thus partakes in the catalytic action of thephotocatalyst (TiO₂). As the charge carriers are formed on the lightactivated titania, electrons migrate to the surface of the photocatalyslto be trapped by the noble metal. The negatively charged noble metalreduces Fe³⁺ to Fe²⁺. Then, Fe²⁺ is oxidized back to Fe³⁺ by thechlorinated compounds at the surface. The process continues without thenoble metal or transition metal oxide deactivation. As such, TiO₂harvests the incoming photons converting them to charge or chargeequivalent. As noted before, the noble metal acts as a mediator totransfer the charge or charge equivalent to target organic species.

[0160] Therefore, it should be understood that in the preferredembodiments of this invention each element or the oxide of each elementis an integral part of the catalytic media. Alternatively, iron canmediate the charge transfer to the platinum when the interaction betweenFe and titania is such to preferentially cause charge transfer to Feupon TiO₂ illumination. Therefore, a synergism exists and can bedescribed for other noble metals and their oxides including Ru, Rh andAg and other semiconductors such as SnO₂, SrTiO₃, WO₃, Fe₂O₃, CdS, ZnO,Ta₂O₅, ZrO₂ and CdSe.

HIGH-FLUX PHOTOCATALYTIC MEDIA OF THE PRESENT INVENTION

[0161] As far as the high-flux applications are concerned, the preferredmedia type and configuration is one that provides highest catalyticactivity at the lowest media temperature. It is to be understood that inthe terminology of this disclosure, the high-flux catalytic media of thepresent invention include the plurality of the catalyst and basematerial (support) that operate in the temperature range ofapproximately 150-400° C. In the preferred embodiment of the presentinvention, the high-flux media is silica, alumina or combination thereofwith well-defined framework and structural features as in zeolites,zeolite-like materials as well as the synthetic aerogel materials.

[0162] In the preferred embodiment of this invention, the catalyticmaterials including the multifunctional Type III (combined photo- andthermocatalyst) and Type V (combined sorbent and thermocatalyst) mediaare used. Yet, in another preferred embodiment of this invention, thebase material is an integral part of or a component of the catalystmaterial, collectively comprising the high-flux catalytic media.

[0163] In one embodiment of the invention, the catalytic media suitablefor use with the high-power UV light sources (e.g. medium-pressuremercury lamps) also include the UV-transparent silica aerogels dopedwith photochemically active compounds (e.g. TiO₂). It is yet anotherpreferred embodiment of this invention to utilize as the high-fluxmedia, co-gelled metal oxide aerogels such as titania-silica aerogelsand transition metal aerogel-supported catalysts (e.g. platinum, nickel,cobalt and copper supported on silica aerogel).

[0164] In another preferred embodiment of this invention, the catalyticmedia composed of chromium and cobalt-exchanged zeolite-Y andchromium-exchanged ZSM-5 (molecular sieve) is used. Yet, in anotherembodiment of this invention, multifunctional catalysts such as thenoble or base metal supported on TiO₂ or ZrO₂ and doped with one or morepromoters chosen from the group of elements: Mo, W, V, and La, is used.

RATIONALE OF THE INVENTION

[0165] Among UV/AOTs, titania-based processes are of particular interestsince they generally do not require added or otherwise consumablechemicals. Volumes have been written on the efficacy of UV-excitedtitania and other bandgap photocatalysts for treatment of organics inwater and air. Despite all that, to date, no commercially viableUV/TiO₂-based pollution control device has been successfullymass-marketed. This is particularly true for applications involvingaqueous-phase photocatalytic treatment. A review of the prior artreveals many reasons cited as the stumbling blocks to successfulimplementation of pollution control devices based on UV-excited, TiO₂and other bandgap photocatalysts. A short list of the generallyrecognized impediments include:

[0166] Practical problems and poor economics of employing slurriedcolloidal titania in aqueous-phase applications.

[0167] Mass transfer limitations associated with processes that employimmobilized instead of slurried colloidal TiO₂.

[0168] Mass transfer limitations affecting treatment of dilutecontaminated streams.

[0169] Non-uniform irradiance over catalytic surfaces and lighttransmission limitations within photocatalytic reactors of the priorart.

[0170] Higher costs when added oxidants are used in both slurried andimmobilized titania-based processes.

[0171] As noted before, an important consideration is the overall energyefficiency of the photocatalytic service. Due to cost and performanceconsiderations, most detoxification applications require single pass,continuous flow of the contaminant stream. Most photoreactors of theprior art are not able to utilize UV photons effectively, especiallywhen very high DREs are required. This is a manifestation of the“one-pass or single-pass” process requirement that greatly limits theoverall apparent process quantum efficiency (photoefficiency). It isgenerally recognized that, even under the best of conditions (i.e. nomass transfer limitations present and uniform catalyst surfaceirradiance) only a fraction of the maximum energy efficiency realizablecan be obtained. This is especially true when the process DRE requiredis high. The net effect of this loss of process photoefficiency is toraise both the operating and capital costs of the photocatalytictreatment. This is so because generating photons capable of exciting thephotocatalyst requires costly electricity and use of special UV lampshaving electric to UV light energy conversion efficiency of no more than35%, at best.

[0172] Therefore, it can be said that not until an engineering approachis found to eliminate this limitation, it is unlikely that UVphotocatalysis can be implemented, widely, as a viable and costeffective pollution control technology. Thus, it is the object of thepresent invention to substantially improve upon performance of thecatalytic treatment process by:

[0173] (i) Devising a catalytic process that is unaffected by masstransfer intrusions.

[0174] (ii) Ensuring the most uniform irradiance distribution over allcatalytic surfaces.

[0175] (iii) Implementing specially designed and formulated catalyticmedia and process configuration that allow decoupling of the processenergy efficiency from DRE of the target pollutants.

[0176] (iv) Employing multifunctional media that allow combinedphotocatalytic and thermocatalytic activity, whenever desirable.

[0177] (v) Simplifying photoreactor and photoprocess optimization andscale-up.

[0178] Now, the theoretical basis of the subject invention that guidedthe development of the present innovative photosystem designs isdisclosed by considering the axisymetrical configuration 1 a and 1 b ofFIG. 9a and 9 b. The catalytic media of the subject invention comprisingthe low-flux media 20-a can be supported photocatalyst, supportedthermocatalyst or a multifunctional media that is both photocatalyst andthermocatalyst. In a like manner the high flux media 20-b is a fluidizedparticle bed that can be supported photocatalyst, supportedthermocatalyst, or a multifunctional media that is both photocatalystand thermocatalyst. In the preferred embodiments of the presentinvention, the low- and high-flux media (20-a and 20-b) are the Type IVand Type III (or V), respectively. The low-flux reactor in oneembodiment of this invention consists of a tubular cell 10-a in whichthe light source 30-a is placed concentrically along the axis, within aprotective quartz or fused silica sleeve 30-c. In thermocatalytic orhigh-flux case, a heat source 30-b (such as a medium pressure mercurylamp. a heated coil or element, etc.) is placed along the axis andwithin a quartz or fused silica sleeve 30-c, as before. It is notedthat, in the description that follows, the choice of an axisymmetricmedia is for the sake of illustrating the application of the preferredembodiments of this invention. The procedure described below is alsoapplicable to media configurations having non-circular cross section(e.g. rectangular, elliptical, rippled, etc.).

[0179] Referring to configuration 1 a of FIG. 9a, 10-a refers to animpermeable hollow shell (metallic, synthetic polymeric, i.e. DuPont'sTYVEK^(R) and the like), having a closed end 12-a and opposite open-endpassageway 14-a, about a closed mid portion 16-a. A permeable catalyticmedia 20-a (Type IV catalytic material coated onto cotton flannel,synthetic polymeric cloth or woven glass fiber cloth/mesh) has one end22-a connected to shell closed end 12-a, and opposite end 24-a,connected to shell mid portion 16-a Stream A passes into inlet 19-a,passes through the catalytic media 20-a and out end passageway 14-a.

[0180] In a like manner, referring to configuration 1 b of FIG. 9b, 10-brefers to an impermeable rotating drum (i.e. metallic, and the like),having a closed end 12-b and opposite closed end 16-b about an open midportion passageway 14-b. The impermeable rotating drum 10-b housedwithin a stationary plenum vessel 10-c, closed at both ends 6 and 8. Apermeable rotating grid or distributor 18 holds the fluidized particlebed 20-b (Type III or V catalytic media). In the preferred embodiment ofthis invention, rotating grid 18 is fabricated in the form of atruncated cone with a 2-8° taper angle, more preferably about 4° taperangle. Furthermore, the rotating grid 18 is constructed using at least a22 gage perforated sheet metal having at least 50% open area. The insidesurface of the grid 18 is covered with a U.S. Sieve #100 mesh stainlesssteel screen butt-welded to perforated basket at either side and tightlywrapped on the outer surface with one layer of a close-knit glass fibermesh/cloth. The rotating basket or grid assembly 18 has one closed endat 22-b connected to impermeable rotating drum closed end 16-b, andopposite end 24-b, connected at mid portion to fused silica sleeve 30-c.Stream A passes into inlet 19-b through the stationary inlet conduit 21into the space between rotating plates 12-b and 24-b, through permeablerotating grid 18, passes through fluidized catalytic media 20-b and outend passageway 14-b, through stationary exit conduit 23. The rotatingdrum 10-b is supported at the bottom and top by ball (or roller)bearings 25 and 27, respectively. Additional bearings 29 and 31 areprovided at the bottom and top to support rotating fused silica sleeveassembly 30-c. Special fluid-tight seals are also provided at theinterfaces between the rotating and stationary articles at 33, 35, 37and 39. The UV lamp 30-b is stationary, so are the connecting powerleads 41 and 43. The lamp coolant (air or nitrogen) enters at 50 throughrotating metallic (e.g. stainless steel) inlet tubing 40 and exits at 55through the rotating metallic (e.g. stainless steel) outlet tubing 45.Finally, the gear system 65 delivers the torque 60 developed by anelectrical motor to gear 70 connected to the rotating inlet conduit 75.

[0181] The fluid containing contaminant A enters the catalytic media20-a in FIG. 9a. It flows radially outward through the catalytic mediaand then along the reactor axis, in the space between the catalyticmedia and reactor wall, and out of the rector at the opposite end. In alike manner, the contaminated stream enters the high-flux reactorradially through the grid and centrifugal fluidized particle bed andexits the reactor axially at one open end of the rotating drum. Both thelow-flux and high flux reactors of FIG. 9a and 9 b can operate eitherhorizontally or vertically, independent of direction of gravitationalacceleration.

[0182] It is understood that the analysis disclosed below is equallyvalid if the direction of the flow that enters and exits the low-fluxreactor is reversed (i.e. contaminated stream entering the catalyticmedia from the dark side of the photosystem). In certain applications,it is desirable or advantageous to have the contaminant stream flow incrossing the catalytic media from the space between the catalytic mediaand reactor wall (dark side) to the space between catalytic media andheat/light source (light side). One example is when the incoming flowcontains dust, particulate matter, or compounds detrimental to thecatalyst activity. In the case of high-flux reactor, the fluidcontaining contaminant A must always enter the high-flux catalytic mediaof FIG. 9b from the dark side of the rotating particle bed. Finally, itshould be noted that the analysis below follows the same line of logicregardless of whether a low-flux or a high-flux reactor is present, orwhether or not the target species cross the light side to the dark sideor vice versa Now let:

[0183] In FIG. 9a and 9 b, Q_(l) refer to flow rate of contaminatedstream A.

[0184] C_(A0) be inlet concentration of target pollutant A.

[0185] C_(Af) be exit concentration of target pollutant A.

[0186] D₀ be the mean diameter of the low-flux catalytic media 20-a inFIG. 9a or high-flux catalytic media 20-b in FIG. 9b.

[0187] d∀ be low and high-flux incremental volume for analysis.

[0188] L be the length of low-flux media 20-a in FIG. 9a or height ofthe high-flux fluidized catalytic media 20-b in FIG. 9b.

[0189] z be the coordinate distance from inlet 19-a in FIG. 9a or theclosed end of the rotating basket/grid 24-b in FIG. 9b.

[0190] dz be the incremental length of the control volume being analyzedin FIG. 9a and 9 b.

[0191] Furthermore, let's consider an irreversible surface reaction onthe catalytic media. Assuming steady state conditions prevail, thematerial balance for species A in the elemental reactor volume d∀ can bewritten as $\begin{matrix}{{{- Q_{1}}\frac{C_{\Delta}}{z}} = {\left( {- r_{AS}} \right) = {{rate}\quad {of}\quad {disappearance}\quad {of}\quad {reactant}\quad A}}} & (1)\end{matrix}$

[0192] Where Q_(l) is the volumetric flow rate (actual), C_(A) is thebulk concentration of species A, and r_(AS) refers to the rate ofreaction of species A on the catalyst surface The rate of the reaction,r_(AS), expressed per unit mass of catalyst, may be written either interms of the diffusion rate from the bulk fluid to the catalyst surfaceor in terms of the rate on the surface as follows:

(−r _(AS))=k _(m) a _(L)(C ₄−C_(AS))=k _(AS) δ′C° _(AS)(αq_(i))^(m)  (2)

[0193] Where;

[0194] C_(AS)≡concentration of species A on the catalyst surface

[0195] k_(m)≡mass transfer coefficient from fluid to catalyst surface

[0196] k_(AS)≡reaction rate constant per unit mass of catalyst

[0197] a_(L)≡mass/heat transfer area per unit length of the catalyticmedia

[0198] δ′≡Mass of catalyst per unit length of the catalytic media

[0199] For radial/lateral flow through catalytic media, it can be saidthat, k_(AS)δ′ is very much less than k_(m)a_(L). Under theseconditions, the mass transfer resistance is negligible with respect tothe surface reaction rate, i.e., the kinetics of the surface reactioncontrol the rate. Then, C_(AS) approaches C_(A) in the bulk fluid, andthe rate is

(−r _(AS))≈k _(AS) δ′C° _(A)(αq _(i))^(m)  (3)

[0200] In equation (3), the term (αq_(l))^(m) represents the photoniccontribution to the reaction rate of species A on the photocatalyticsurface. In the case of a purely thermocatalytic media, equation (3)reduces to

(−r _(AS))=k _(AS) δ′C° _(A)  (4)

[0201] Exponent p and m represent reaction orders with respect to theconcentration of species A and photons capable of exciting thephotocatalyst. Clearly, in certain situations, the assumption thatC_(AS)=C_(A) may not be valid. In those situations C_(AS) is determinedin terms of the bulk concentration of species A. The rate of consumptionof pollutant A on the surface of the catalyst can then be described bythe Langmuir-Hinshelwood-Hougen-Watson (LHHW) formulation. For example,if the reaction at the surface is irreversible, involves only species Aand product P of the reaction is very strongly adsorbed but adsorptionof the reactant A is relatively week, then, the rate equation becomes:

(−r _(AS))=k′ _(AS) δ′C _(a) /C _(P)

[0202] Another example is when the reacting molecules, intermediateproducts (or secondary reactants) or final reaction products arestrongly adsorbed on the surface. This is the case when treatingplasticizers such as diethyiphathalate (DEP) or d-in-propyladipate(DPA). Oxidation of DEP and DPA on the surface of titania proceeds byway of phathalic acid (PA) and adipic acid (AA), respectively, as theintermediate products. PA and AA are strongly adsorbed on the catalystsurface. However, if the oxidant is present in excess or theconcentration of pollutant A is low, and all other contaminants presentadsorb very weakly, then, equation (3) is valid and p≈1. From equation(1) and (3,we have $\begin{matrix}{{Q_{1}\frac{C_{A}}{z}} = {{- k_{AS}}\delta^{\prime}{C_{A}\left( {\alpha \quad q_{1}} \right)}^{m}}} & (5)\end{matrix}$

[0203] Equation (5) is solved, subject to the following boundaryconditions:

[0204] C_(A)=C_(A0) at z=0; and, C_(A)=C_(Af) at z=L

[0205] to yield $\begin{matrix}{\frac{C_{Af}}{C_{A0}} = {{\exp \left\lbrack {- \frac{k_{AS}\delta^{\prime}{L\left( {\alpha \quad q_{1}} \right)}^{m}}{Q_{1}}} \right\rbrack}.}} & (6)\end{matrix}$

[0206] Where; C_(A0) and C_(Af) refer to the bulk fluid concentration ofspecies A at the reactor inlet and outlet and L is the reactor/catalyticmedia length. In terms of conversion, x_(m), so equation (6) can berewritten to give $\begin{matrix}{{x_{m} \equiv {1 - \frac{C_{Af}}{C_{A0}}}} = {1 - {\exp \left\lbrack {- \frac{k_{AS}\delta^{\prime}{L\left( {\alpha \quad q_{1}} \right)}^{m}}{Q_{1}}} \right\rbrack}}} & (7)\end{matrix}$

[0207] The apparent quantum efficiency of the photoprocess, ø_(l), isdefined as $\begin{matrix}{\varphi_{1} \equiv \frac{\left( {- r_{AS}} \right)}{\pi \quad D_{0}\alpha \quad q_{1}}} & (8)\end{matrix}$

[0208] Where

[0209] q_(i)≡irradiance on the catalytic surface

[0210] α≡absorptivity of photocatalyst material

[0211] D₀≡mean diameter of the catalytic media 20-a or 20-b in FIG. 9aand FIG. 9b, respectively, as before.

[0212] Here, r_(AS) is defined as the rate of reaction per unit lengthof catalytic media Then, substituting for (−r_(AS)) from equation (3)into equation (8) and noting: p=1, we have $\begin{matrix}{\varphi_{1} \equiv {\frac{k_{AS}\delta^{\prime}C_{4}}{\pi \quad D_{0}}\left( {\alpha \quad q_{1}} \right)^{m - 1}}} & (9)\end{matrix}$

[0213] At the onset, ø≡ø₀ and C_(A)≡C_(A0), so that $\begin{matrix}{{\varphi_{0} \equiv {\frac{k_{AS}\delta^{\prime}}{\pi \quad D_{0}}\left( {\alpha \quad q_{i}} \right)^{m - 1}C_{A0}}}{or}{{k_{AS}{\delta^{\prime}\left( {\alpha \quad q_{i}} \right)}^{m}} = \frac{\pi \quad D_{0}\alpha \quad q_{i}\varphi_{0}}{C_{A0}}}} & (10)\end{matrix}$

[0214] Substitute from equation (11) into equation (6) and (7) to get$\begin{matrix}{{\frac{C_{Af}}{C_{A0}} = {\exp \left( {- \frac{\varphi_{0}\alpha \quad W_{uv}}{Q_{1}C_{A0}}} \right)}}{and}} & (12) \\{x_{m} = {1 - {\exp \left( {- \frac{\varphi_{0}\alpha \quad W_{uv}}{Q_{1}C_{A0}}} \right)}}} & (13)\end{matrix}$

[0215] Where, W_(uv)≡πD₀q_(l) refers to the ultraviolet (all wavelengthsat or below that needed to excite the photocatalyst) power output of thelamp 30-a in FIG. 9a or 30-b in FIG. 9b. Now, let $\begin{matrix}{\eta \equiv \frac{\alpha \quad W_{uv}}{Q_{1}C_{A0}}} & (14)\end{matrix}$

[0216] Then, equation (12) and (13) can be rewritten as $\begin{matrix}{{\frac{C_{Af}}{C_{A0}} = {\delta_{f} = {\exp \left( {- {\eta\varphi}_{0}} \right)}}}{{Where},{{{by}\quad {definition}\text{:}\quad \delta_{f}} = {C_{Af}/C_{A0}}},{{and}\quad {then}}}} & (15) \\{x_{m} = {1 - {{\exp \left( {- {\eta\varphi}_{0}} \right)}.}}} & (16)\end{matrix}$

[0217] The process photo-efficiency ø can be expressed in terms of ø₀,as $\begin{matrix}{{{\frac{\varphi_{1}}{\varphi_{0}} \equiv \frac{\frac{k_{AS}\delta^{\prime}}{\pi \quad D_{0}}\left( {\alpha \quad q_{i}} \right)^{m - 1}C_{Af}}{\frac{k_{AS}\delta^{\prime}}{\pi \quad D_{0}}\left( {\alpha \quad q_{i}} \right)^{m - 1}C_{A0}}} = {\frac{C_{Af}}{C_{A0}} \equiv \delta_{f}}}{Then}{\frac{\varphi_{1}}{\varphi_{0}} \equiv \frac{C_{Af}}{C_{A0}} \equiv \delta_{f} \equiv {1 - x_{m}}}} & (17)\end{matrix}$

[0218] Thus

ø_(l)≡ø₀(1−x _(m))=ø₀δ_(f)  (18)

[0219] Equation (17) and (18) imply that in a single-stage low- andhigh-flux photocatalytic reactors 1 a of FIG. 9a and 1 b of FIG. 9b, thesingle-component conversion efficiency x_(m) is always coupled to theapparent process photo-efficiency ø₁ (=ø₀δ_(f)). The “coupling” equation18 also implies that as the process DRE→100% (i.e. x_(m)→1), thesingle-stage photoefficiency approaches zero (ø_(l)→0). This is aninherent deficiency of the photocatalytic processes that results inlower and lower photo-efficiencies (poor energetics) at increasinglyhigher and higher process DREs. A method for mitigating this effect and,thus, decoupling ø_(l) from x_(m), constitutes the essence of thepresent invention, disclosed in the following pages. From equation (16),write $\begin{matrix}{\frac{x_{m}}{\eta} = {\varphi_{0}{\exp \left( {- {\eta\varphi}_{0}} \right)}}} & (19)\end{matrix}$

[0220] Combining equation (18) and (19) gives${\varphi_{1} \equiv \frac{x_{m}}{\eta} \equiv {- \frac{\delta_{f}}{\eta}}} = {\varphi_{0}\delta_{f}}$

[0221] Also

ø₁/ø₀=(dx _(m) /dη)/(dx _(m) /dη)_(at n=0)=1−x _(m)=δ_(f)  (20-a)

[0222] Alternatively, the generalized form of the coupling equation canbe written as

ø₁/ø₀=(dδ _(f) /dη)/(dδ _(f) /dη)_(at η=0)=1−x _(m)=δ_(f)  (20-b)

[0223] Finally, for purely thermocatalytic media, combining equation (4)to (7) gives $\begin{matrix}{x_{m}^{\prime} \equiv {1 - {\exp \left\lbrack {- \frac{\left( {- r_{AS}} \right)_{\max}L}{Q_{1}C_{A0}}} \right\rbrack}}} & (21)\end{matrix}$

[0224] Where, (−r_(AS))_(max) refers to the maximum value ofthermocatalytic reaction rate that is

(−r _(AS))_(max) =k′ _(AS) δ′C _(A0)  (22)

[0225] and $\begin{matrix}{k_{AS}^{\prime} \equiv {A\quad {\exp \left( \frac{E}{R_{g}T} \right)}}} & (23)\end{matrix}$

[0226] Where, A is the frequency (or pre-exponential) factor and E isthe activation energy. R_(g) refers to ideal gas constant.

[0227] Noting that, surface (“heterogeneous”) Damkohler member, Da, isdefined as $\begin{matrix}{{Da} \equiv \frac{\left( {- r_{AS}^{\prime}} \right)L}{Q_{1}C_{A0}}} & (24)\end{matrix}$

[0228] Then, equation (21) can be rewritten as

x′ _(m)≡1−exp (−Da).  (25)

[0229] For the general case wherein the catalyst media 20-a of FIG. 9aand 20-b of FIG. 9b may be active as either photocatalyst orthermocatalyst, combining equation (16) and (25) yields

x _(m)=1−exp[−(ηø₀ +Da)]  (26)

[0230] Equation (26) represents the general case of the photocatalytic,thermocatalytic or combined photo- and thermocatalytic processconversion efficiency subject to no mass transfer limitations. Equation(26) can be rewritten as

x _(m)≡1−δ_(f)≡1−exp[−(ηø₀ +Da)]

[0231] where, as before $\begin{matrix}{\delta_{f} \equiv \frac{C_{Af}}{C_{A0}}} & (27)\end{matrix}$

[0232] Then

δ_(f)=exp[−(ηø₀ +Da)]  (28)

[0233] From equation (14) $\begin{matrix}{{\eta \equiv \frac{\alpha \quad W_{uv}}{Q_{1}C_{A0}} \equiv \frac{a}{Q_{1}C_{A0}} \equiv {aH}}{Where}} & (29) \\{{H \equiv \frac{1}{Q_{1}C_{A0}}}{and}} & (30) \\{{{Da} \equiv \frac{\left( {- r_{AS}^{\prime}} \right)L}{Q_{1}C_{A0}}} = {\left( {- r_{AS}^{\prime}} \right){LH}}} & (31)\end{matrix}$

[0234] Then

1−x _(m)≡δ_(f)≡exp[−(ηø₀ +Da)]=exp[−(aø ₀ −r′ _(AS) L)H]  (32)

[0235] In equation (32), “a” is a parameter whose value depends on theunits of Q_(l), C_(A0), and W_(uv) as well as the type of light sourceemployed Q_(l), C_(AO0) and W_(uv) are given in units of Ls⁻¹, ppmv andmW, respectively. In equation (32), “a” is equal to 1062 and 122,543 fortypical low-pressure pressure mercury lamp 30-a (60 inch arc length and32% electric to photon energy efficiency) and medium-pressure mercurylamp 30-b (60 inch arc length, 200 W/in output and 20% electric tophoton. λ<400 nm energy efficiency), respectively. Again, equation (32)represents conversion for the general case of a photocatalytic,thermocatalytic or combined photo- and thermocatalytic process that is

[0236] 1—Free from mass transfer intrusions.

[0237] 2—Provides uniform catalytic media surface irradiance

[0238] 3—Results in a uniform catalyst temperature.

[0239] The coupling equation (20) now takes the following form:

x _(m)≡1−δ_(f)≡1−(dx _(m) /dH)/(dx _(m) /dH)_(at H=0)  (33)

[0240] Again, equation (33) applies if the photocatalytic orthermocatalytic process is free from the mass transfer intrusions andall catalytic surfaces are uniformly irradiated or heated. The low- andhigh-flux catalytic media/processes of the present invention all conformto the requirements of equation (32) and (33), as depicted by thefollowing examples.

EXAMPLES 4 & 5

[0241] EXAMPLES 4 and 5 describe the low-flux data obtained by thesubject inventor using small-gap annular and fluidized bedphotocatalytic reactors. These EXAMPLES are intended to show that if, bydesign, no mass transfer intrusions exists within photoreactor, then,equation 32 describes species conversion, regardless of the reactor typeand fluid-solid contacting scheme.

[0242] EXAMPLE 4 refers to small gap annular reactor tests. The reactorbody was a Pyrex^(R) tube having 38 mm outside diameter and a nominallength of 90 cm A standard, Voltarc Tubes, Inc. G36T6 germicidallow-pressure mercury vapor lamp was placed co-axially within the Pyrextube. Titania (Degussa P25) wash coated onto the inner surface of thephotoreactor. The reactor volume was 808 ml; flow passage (gap betweenthe inner wall of the reactor and quartz sleeve encasing LPML) was 3.5mm and catalyst geometrical surface area totaled 1531 cm². Air streamcontaining 845 and 85 ppmv ethanol vapor entered the annularphotoreactor. All reactor walls were kept at a constant temperature ofabout 85° C.

[0243] EXAMPLE 5 refers to a standard 1 g (acceleration of gravity,9.8066 m(s²) fluidized bed (1 gSFB) photoreactor tests. The bedmaterials consisted of fine silica-gel particles that provided the basematerial for titania photocatalyst. The photocatalyst was deposited onthe silica-gel particles by soak & dry technique. After wash coatingsilica particles, they were baked at 450° C. for several hours beforeuse. The catalyst loading for these tests was approximately 20-wt %. Thepacked bed thickness for EXAMPLE 5 tests were about 11 mm and meanparticle size fell in the range of 100-120 mesh (U.S. standard sievesizes). The expanded bed volume was measured to be approximately 15.3ml. The diameter of the quartz grid (distributor) was 40 mm. The fusedsilica fluidized bed tube was placed inside a photon bucket surroundedby six 8 W low-pressure mercury lamps. LPMLs could be turned on in banksof 2, 3, 4, and 6 lamps.

[0244]FIG. 10 depicts ethanol conversion results for the low-flux flowphotoreactor of EXAMPLES 4 and 5. It can be seen that ethanol conversiondata obtained within the small gap (3.5 mm) annular and 1 g fluidizedbed (11 mm thick particle bed) photoreactors closely conform to the plugflow approximation given by equation 32. In a like manner. all thelow-flux catalytic media and photoreactors of the present invention alsoconform to plug-flow approximation given by equation (32) and (33). Thiswill be demonstrated by EXAMPLES 7-12, later in the text. But first, wedisclose the preferred embodiments and design criteria for thesingle-stage, high-flux rotating fluidized bed reactors of the presentinvention as follows.

EXAMPLE 6

[0245] The governing equations for designing the preferred high-fluxrotating fluidized bed reactors of the present invention are as follows:

ΔP _(FB) =m _(B1)ω₀ ²/2πL  (34) $\begin{matrix}{{Ga} = {{\left\lbrack \frac{150\left( {1 - ɛ_{B}} \right)}{ɛ_{B}^{3}\varphi_{S}^{2}} \right\rbrack {Re}_{MF}} + {\frac{1.75}{ɛ_{B}^{3}\varphi_{S}}{Re}_{MF}^{2}}}} & (35)\end{matrix}$

Q ₁=ρ_(f) u ₁ A _(gnd)=ρ₁ u ₁ πD ₀ L  (36)

[0246] Where; $\begin{matrix}{{Ga} = {{{Galileo}\quad {Number}} = {\left( {\frac{\rho_{S}}{\rho_{J}} - 1} \right)\omega_{0}^{2}D_{0}\frac{\overset{\_}{d_{P}^{3}}}{v_{j}^{2}}}}} & (37) \\{{Re}_{MF} = {{{Reynolds}\quad {Number}} = \frac{u_{MF}\overset{\_}{d_{P}}}{v_{f}}}} & (38)\end{matrix}$

[0247] In equations 34 to 38, ΔP_(FB), m_(B1), ω₀, ε_(B), ø_(S), ρ_(S),{overscore (d)}_(p), ρ_(f), V_(f), u_(MF), u_(l), D₀, L, and A_(grid)denote catalyst bed pressure drop, single-stage fluidized bed mass,angular velocity of the grid/basket, bed void fraction, sphericity ofcatalyst particle, particle density, mean particle diameter, fluiddensity, fluid kinematic viscosity, minimum fluidization velocity,superficial fluid velocity at grid surface, diameter of rotatinggrid/distributor, bed height, and grid surface area, respectively. Theminimum fluidization velocities in centrifugal fluidized bed reactorsare based on a correlation given by equation (36) due to Levy, E. K.,Martin, N. and J. C. Chen, Fluidization, Edited by F. Davidson and D. L.Kearins, Cambridge University Press, London, p.71 (1978), which isincorporated herein by reference.

[0248] General guidelines for designing high-flux, multi-stagecentrifugal fluidized bed photocatalytic, thermocatalytic and combinedphoto and thermocatalytic reactors of the present invention based on theequations above are as follows:

[0249] 1. Process conditions are so chosen to facilitate plug-flowbehavior for species transported across the particle bed. This requiresthat the superficial fluid velocity to remain near minimum fluidizationvelocity u_(MF) all the time. In the preferred embodiment of thisinvention, u₁ varies between 2 and 4 times u_(MF). For reactorthrough-puts much beyond 4u_(MF), the extent of bubble formation andfluid by-pass is considerable.

[0250] 2. With reference to equation (34), it is important to have largeL but small m_(B1) and ω₀. Large L also favors irradiance on the bedsurface (refer to FIG. 2 and note large L/D_(l)). The requirement forsmall bed mass can also be satisfied in most cases. Considering limitedpenetration of UV light across fluidizing particle bed of mostly opaquecatalyst material, an expanded bed thickness of approximately 5-20 mm(depending on the mean particle diameter, bed void fraction, etc.) isnormally sufficient. Bed angular velocity is related to reactorthroughput via equation (35).

EXAMPLE 7

[0251] EXAMPLES 7 to 12 describe the preferred embodiments of thepresent invention with regard to the low-flux catalytic mediaimplementation at single cell, plurality of multiple cells (or banks)and unit (multiple banks) levels. FIG. 11a and 11 b depict one preferredembodiment 100 of the low-flux catalytic media implementation of thepresent invention wherein the catalytic process occurs within a singletubular metallic cell 110. With reference to FIG. 11a, the main reactorbody 110 is constructed from seamless 6061-T6 (aerospace grade) aluminumtube, 4.5″ OD×4.0″ID×60″ long (LL). Two 6.0″ diameter aluminum end caps116 and 118 are bolted to two aluminum flanges 112 and 114,respectively. The aluminum flanges 112 and 114 are welded to either endof the reactor tube 110. The end caps not only seal the reactor tube,but also provide a means for installation of the photocatalytic stockingas well as the devices necessary for monitoring of the process variables(pressure, temperature, irradiance, etc.). The irradiance levels withinthe reactor are measured in two locations using an International Light,model IL1700/SED005 radiometer 140. Radiometer 140 measures 254 nmradiation with 120-volt power supply 147. Radiometer was mountedparallel to the lamp axis facing a quartz window 141 installed on theinlet end cap 116. Pressure drop across the photocatalytic stocking ismeasured with a differential pressure gauge 144 (Dwyer Niagnehelic)connected with ⅛″ OD PTFE tubing to two static pressure taps 153 and 155attached to the reactor end caps 116 and 118, respectively.

[0252] The preferred light source for this embodiment is a standardlow-pressure mercury vapor lamp such as one commercially available fromVTI, e.g. G64T5VH having 120 volt power supply 131. The ultravioletlight source 130 is placed within a 1 OD quartz or fused silica sleeve132 that is closed in one end The quartz sleeve 132 is mounted alone theaxis of the phototube via a bushing assembly located on the exit end cap118 as depicted in FIG. 11a. The open end of the quartz sleeve 132protrudes from the exit end cap 118 to accommodate lamp's electricalconnections and cooling line 133. Lamp cooling is accomplished bydirecting dry cooling air 133 (provided by an Ingersoll-Rand compressormodel SSRXF50SE 137, FIG. 11b). Typically, 1.5 SCFM of air is fedthrough a ¼″ OD PTFE tubing 134, that extends half way into the quartzsleeve 132 providing the necessary cooling to the UV lamp. This flow ofair was sufficient to maintain lamp's cold spot temperature within theoptimum range and around approximately 51° C. The lamp's cold spottemperature is measured by a type “K” thermocouple 135 attached to thelamp envelope at 139, halfway along its length. Reactor outer walltemperature is monitored with a thermocouple pasted onto the outershell, half way down its length. Temperature monitor 136 gives the skintemperature of the catalytic stocking 120 via thermocouple 145 (attachedto the fabric at 149) and lamp 130 envelope temperature via thermocouple135 (attached to the lamp at 139).

[0253] Referring to FIG. 11a, catalyst/support (base material) 120 ofthe present invention comprised of a tubular cotton fabric onto which asuitable photocatalytic material has been deposited according toteachings of EXAMPLE 3 and Table I. In one preferred embodiment of thepresent invention, the low-flux media 120 is comprised of the wovencotton flannel fabric. Catalytic media 120 connects at one end 122 toflange 112 and has an opposite end 124 connected to an impermeable PTFEend baffle 129. A reagent mixing chamber 158 is used to preparevapor-phase contaminant stream A as depicted in FIG. 11b. Reagents areloaded into two Hamilton™ gas-tight syringes 154 a and 154 b as depictedin FIG. 11b. All syringes have shanks and plungers that are preferablyglass and PTFE construction, respectively. The syringe volume (capacity)depends on the carrier gas flow (e.g. air) and varies between 1 to 50ml. Fully loaded syringes are then placed on a KD Scientific syringepump 160 that pumps reagents (e.g. a mixture of nitroglycerine andacetone as depicted in FIG. 11b) to a Sonics and Materials™ brandultrasonic atomizer probe 152 via a {fraction (1/16)}″ OD PTFE tubing asdepicted in FIG 11 b. The atomizer probe 152 is bolted to a stainlesssteel plate 156 that covers the open end a glass bell jar 150 of themixing chamber 158 as shown in FIG. 11b.

[0254] The mixing chamber 158 comprised of an inverted glass bell jar150 supported at the top by a stainless steel plate 156 and a rounddonut-shaped aluminum ring 157. The heated carrier gas such as airenters at the top of the mixing chamber through a ½″ OD stainless steeltube 162. The atomized liquid is mixed with the carrier gas anddelivered to the reactor via a 1″ OD heated stainless steel line 163.The mixing chamber wall temperature and the gas within are measuredusing type “K” thermocouples 166 and 164, respectively as shown in FIG.11b. A static pressure tap 170 at the top of the mixing chamber allowsgas pressure measurement.

[0255] Now, with reference to FIG. 11b, dry compressed air from 137enters the system through two mass flow controllers 172 and 174 (Porter,model 204A). One portion of the metered air (typically 10 SCFM) passesthrough air heater 176 (Omega, model AHP-7561) and then into the mixingchamber 158. The second portion of the metered air (typically 10.15SCFM) passes through second air heater 178 (Omega, model AHP7561) andafter bypassing the mixing chamber 158, combines with and dilutes itsexit flow as depicted in FIG. 11b. The combined stream enters into thephotocatalytic reactor 110 at A1. According to FIG. 11a, air containingin) contaminant A passes into one end of catalytic media 120 about lamp130 and then in the direction of arrow A2 through sides of catalyticmedia 120 and into the space between 120 and reactor wall 110 at A3 andexit out of the reactor at A4.

[0256] An isokinetic sampling probe 180 is installed just upstream ofthe reactor as depicted in FIG. 11b. Gas collected by the probe passesthrough a Tenax adsorbent tube (Supelco 35/60, Orbo #42) and through arotameter 184 (Gilmont Accucal) for quantification. Typical samplingvolume is 27 liters, collected at about 1.8 L/min for 15 min. Thereactor effluent is sampled via 182 and 186, as depicted in FIG. 11b, ina manner similar to that described above for the reactor inlet stream.The sampling flow rate at the exit is lower than that at the inlet dueto lower exit port pressure. A portion of the exit gas is diluted withair (31:1) and then fed to a chemiluminescence NO_(x) analyzer 186(TECO, model 42) for real time monitoring of NO and NO₂ concentrations.NO_(x) data is acquired using a PC based data acquisition system 188(Workbench PC. Strawberry Tree, Inc.) as shown in FIG. 11b.

[0257] The EPA method 5 and OSHA method 43 (or NIOSH-2507 method) areemployed, wherever applicable, to sample and analyze the inlet andoutlet reagent concentration. The less volatile organic compounds aretrapped within absorbent tubes supplied by Supelco company. Isokineticsampling probes are used with the less volatile compounds. Theanalytical system consists of a capillary gas chromatograph (GC),connected to a Varian Saturn II ion-trap mass spectrometric system. TheGC column used is a J & W fused silica capillary column, 15 m long, ¼ mmID, with 1 micron coating of DB-1. Fixed gases and volatile organiccompounds are analyzed on a packed column (30 feet, ⅛″ OD Hayesep D_(B))using Varian GC 3400 equipped with flame ionization and thermalconductivity detectors.

EXAMPLE 8

[0258] The article of EXAMPLE 7 wherein the reagent solution was 5% byweight nitroglycerin (NCG) in acetone (DMK). The carrier as was heatedair (approximately 85° C.) flowing at 8 standard cubic feet per minute(SCFM). The average outside diameter of the catalytic stocking 120 usedwas 3.5 inches.

EXAMPLE 9

[0259] The article of EXAMPLE 7 wherein the reagent solution contained5% by weight nitroglycerin in acetone. The carrier gas comprised of airheated to 90° C. and flowing at 8 SCFM into the mixing chamber 158 andphotocatalytic reactor 110 (FIG. 11b). The material of the catalyticmedia or stocking 120 was woven cotton duck fabric, having an OD of 2.75inches.

EXAMPLES 10 to 12

[0260] The article of EXAMPLE 7 wherein the reagent solution contained2-nitrodiphenylamine (2NDPA) stabilized nitroglycerin. The reagentdelivery system was a U-shaped glass tube packed with glass wool andfilled with a mixture of NG and 2NDPA solution. The carrier gas washeated air at 90° C. flowing at 8, 10 and 12 SCFM corresponding toEXAMPLES 10, 11, and 12, respectively. The low-flux media (catalyticstocking) 120 was woven cotton flannel (both sides brushed) having an ODof 3.75 inches.

EXAMPLE 13

[0261] This Example demonstrates the performance of a single-stagephotocatalytic stocking (SSPCS). Base material/support for this SSPCSwas super flannel cotton, having an OD of about 3.8 inches, preparedaccording to the teachings of EXAMPLE 1. The catalytic media of thisexample was Kemira UNITI-98 prepared according to instructions ofEXAMPLE 2 with no additives or further modifications. The SSPCS wasprepared in a manner described in EXAMPLE 3. The SSPCS was tested in thelow-flux reactor of FIG. 11 according to the methods and proceduresdescribed in EXAMPLE 7 and 9. Briefly, the reazent solution usedcontained 5% by weight nitroglycerine in acetone. The carrier gascomprised of air heated to about 95° C. and metered at 15.5 SCFM(approximately 20.2 ACFM at the average reactor temperature) enteringinto the reagents mixing chamber 158 and then into the photocatalyticreactor 110 (FIG. 11b). Concentration of nitroglycerin in the gas-phasewas approximately 9.0 ppmv. The nitroglycerine DRE measured atapproximately 75% (≈79.5% at the exit). The residence time for NG withinthe catalytic media was determined to be approximately 36 ms. Additionof some additives from TABLE I improves performance. For example, addingorganic Saffron gives approximately 78% NG DRE (≈81.5% at the reactorexit) for an NG inlet concentration of 10 ppmv but all otherexperimental conditions identical to that of the base-case testdescribed above.

[0262]FIG. 12 depicts the laboratory flow reactor data of the EXAMPLES 8to 12 for photocatalytic conversion of nitroglycerin in air. The plugflow behavior of the singe-cell reactor of EXAMPLE 7 is depicted andindicates the validity of equations 32 and 33, described before. Thequantum efficiency at the onset, ø₀, for nitroglycerin vapors in air wasestimated from the laboratory data of EXAMPLES 8 to 12 as displayed inFIG. 12 to be approximately 25%. In EXAMPLE that follows a method formitigating the coupling effect and thus permitting partial or fulldecoupling of ø from x_(m) (or δ_(f)) is disclosed.

EXAMPLE 14

[0263] EXAMPLE 14 describes the preferred embodiments of the presentinvention for designing multi-stage catalytic media for both low-fluxand high-flux applications. Let's consider a segmented photocatalytic,thermocatalytic or combined photo and thermocatalytic media that willallow multiple contact between the contaminated stream and the catalyst.The catalytic media within a single-cell can be partitioned in a mannerthat either maximizes the quantum efficiency of the process or minimizesthe pressure drop across the cell.

[0264] The underlying principles for designing multistage catalyticmedia are disclosed with reference to FIG. 13a that depicts a singlemultistage photo-cell 1300 having unequally partitioned media. In FIG.13a, a longitudinal impermeable shell 1304 with inlet end 1302 andoutlet end 1306 and UV lamp 1309 having protective sleeve 1308 arecoaxially mounted. The first catalytic media 1310 inside the shell hasone end 1312 connected to the inlet 1302 of the impermeable shell 1304and an opposite end 1316 connected to the UV lamp sleeve 1308 atdistance l₁. A second catalytic media 1320 has one end 1322 connected toinside the shell 1304 and an opposite end 1326 connected to the UV lampsleeve 1308 at distance l₂. The third catalytic media 1330 is connectedsimilarly at distance 1 ₃ and the n^(th) catalytic media 13 n 0 isconnected at distance l_(n). The length 1 ₁ of the first media isgreater than the length l₂ of the second media and so forth. Each mediasegment forms a different stage (i.e. stage 1, stage 2, stage 3, . . . .stage n). Fluid carrying contaminant A flows into inlet end 1311 of thefirst media 1310 through sides of first media to a space between themedia 1310 and the impermeable shell 1304 and then similarly into theother media 1320, 1330, . . . , 13n0, respectively until it exits fromthe outlet end 1306 of the impermeable shell 1304. Now, with referenceto FIG. 13a, rewrite equation (32) in the following form:$\begin{matrix}{{{\ln \quad \delta_{f}} \equiv {{- \left( {{a\quad \varphi_{0}} - r_{AS}^{\prime}} \right)}H} \equiv {- \frac{\left( {{a\quad \varphi_{0}} - r_{AS}^{\prime}} \right)}{Q_{1}C_{A0}}}}{or}{Q_{1} \equiv {- \frac{\left( {{a\quad \varphi_{0}} - r_{AS}^{\prime}} \right)}{C_{A0}\ln \quad \delta_{f}}}}} & (39)\end{matrix}$

[0265] Again, Q_(l) refers to the flow rate of contaminant streamthrough a simple, single stage catalytic media (also termed stocking orcartridge in the case of the low-flux application). For the more generalcase of a catalytic media having “n” unequal stages, equation (32) takesthe following form: $\begin{matrix}{\delta_{i + 1} \equiv {\delta_{i}\exp \left\{ \frac{{- \left( {{a\quad \varphi_{0}} - r_{AS}^{\prime}} \right)}\lambda_{i + 1}}{Q_{n}C_{A,i}} \right\}}} & (40)\end{matrix}$

[0266] Where:${\delta_{l} \equiv \frac{C_{A,i}}{C_{A0}}},{\delta_{i + 1} \equiv \frac{C_{A,{i - 1}}}{C_{A0}}},{\lambda_{i + 1} \equiv \frac{l_{i - 1}}{L}},$

[0267] and Q_(n) denotes the contaminant flow rate within a photocellhaving n unequal stages (as in FIG. 13a). Combining equation (39) and(40), to get $\begin{matrix}{{\delta_{i + 1} \equiv {\delta_{i}{\exp \left( \frac{\lambda_{i + 1}\ln \quad \delta_{f}}{\psi_{n}\delta_{i}} \right)}}}{Where}} & (41) \\{\psi_{n} \equiv \frac{Q_{n}}{Q_{1}}} & (42)\end{matrix}$

[0268] ψ_(n) is a monotonic function of n and as n→∞, ψ_(n)→ψ_(∞),asymptotically, where $\begin{matrix}{\psi_{\infty} \equiv \frac{Q_{\infty}}{Q_{1}} \equiv {- \frac{\ln \quad \delta_{f}}{1 - \delta_{f}}}} & (43)\end{matrix}$

[0269] Equation (43) can be readily proved by first considering equation(36) and noting that as n→∞, λ_(i)→l/n=ε, thus${y(ɛ)} = {\frac{\delta_{i}}{\delta_{i - 1}} = {\exp \left( \frac{ɛ\quad \ln \quad \delta_{f}}{\psi_{\infty}\delta_{i - 1}} \right)}}$

[0270] Now, consider the Taylor expansion of the y(ε) in terms of ε asε→0, and neglecting ε² and all higher order terms, to get${y(ɛ)} = {{\frac{\delta_{i}}{\delta_{i - 1}} \approx {1 + \frac{ɛ\quad \ln \quad \delta_{f}}{\psi_{\infty}\delta_{i - 1}}}} = \frac{\ln \quad \delta_{f}}{n\quad \psi_{\infty}\delta_{i - 1}}}$Then${\delta_{i} - \delta_{i - 1}} = {{{- d}\quad \delta} = \frac{\ln \quad \delta_{f}}{n\quad \psi_{\infty}}}$

[0271] But

δ_(i)=δ₀−idδ=1−idδ

[0272] Likewise, for the n^(th) term to get

δ_(n)=δ₀−ndδ=1−ndδ

[0273] But, δ_(n)=δ_(f), and${d\quad \delta} = {- \frac{\ln \quad \delta_{f}}{n\quad \psi_{\infty}}}$Then $\delta_{f} = {1 + \frac{\ln \quad \delta_{f}}{\psi_{\infty}}}$Thus $\psi_{\infty} = {- \frac{\ln \quad \delta_{f}}{1 - \delta_{f}}}$

[0274] This is equation (43) noted before. In this equation, ψ_(∞) is afunction of δ_(f) only, i.e. at a given δ_(f), equation (43) sets theceiling (upper limit) on the extent of the multi-stage reactorperformance. In a way, full decoupling is possible only if the catalyticcartridge contains infinite number of reaction stages. For all othercases for which a finite number of partitions are made, only partialdecoupling will be obtained.

[0275] It is easy to show that as n→∞, the apparent quantum efficiencyof the process always approaches ø₀ (i.e. ø_(∞)→ø₀) Combine equation(39) and (43) to get$Q_{\infty} = {{- \frac{Q_{1}\ln \quad \delta_{f}}{1 - \delta_{f}}} = \frac{a\quad \phi_{0}}{\left( {1 - \delta_{f}} \right)C_{A0}}}$Then ${1 - \delta_{f}} = \frac{a\quad \phi_{0}}{Q_{\infty}C_{A0}}$Also, from  equation  (29) $\eta_{\infty} = \frac{a}{Q_{1}C_{A0}}$

[0276] Then

1−δ_(f)=ø₀η_(∞)

[0277] Finally, from equation (20), written in terms of δ_(f) (insteadof x_(m))$\frac{\phi_{\infty}}{\phi_{0}} = {\frac{\left( \frac{\delta_{f}}{\eta_{\infty}} \right)}{\left( \frac{\delta_{f}}{\eta_{\infty}} \right)_{{{as}\quad \eta}\rightarrow 0}} = {\frac{- \phi_{0}}{- \phi_{0}} = 1}}$

[0278] As discussed before, in equation (43), Q_(∞) refers to thecontaminant flow rate across the catalytic media having an infinitenumber of stages (or compartments). Also, equation (43) provides theupper limit of performance for a single-cell photocatalytic,thermocatalytic or combined photo- and thermocatalytic reactor.

[0279] Now, again, with reference to FIG. 13a, write${\frac{\delta_{i}}{\delta_{i - 1}} = {\exp \left( \frac{\lambda_{i}\ln \quad \delta_{f}}{\psi_{n}\delta_{i - 1}} \right)}};{i = {1\quad {to}\quad {n.}}}$

[0280] Subject to following three constraints:

λ₁+λ₂+ . . . +λ_(n)=1; δ₀=1; δ_(n)=δ_(f)

[0281] Then $\begin{matrix}{{\psi_{n} \equiv \frac{\ln \quad \delta_{f}}{\sum\limits_{i = 1}^{n}{\delta_{i - 1}{\ln \left( \frac{\delta_{i}}{\delta_{i - 1}} \right)}}}}{or}{\psi_{n} \equiv \frac{\ln \quad \delta_{f}}{{\ln \quad \delta_{1}} + {\sum\limits_{i = 2}^{n}{\delta_{i - 1}{\ln \left( \frac{\delta_{i}}{\delta_{i - 1}} \right)}}}}}} & (44)\end{matrix}$

[0282] Subject to constraint:

δ_(n)=δ_(f)  (45)

[0283] Here, the objective is to maximize the normalized throughputψ_(n)≡Q_(n)/Q_(l) subject to the constraint of equation (45). Aconvenient method for solving an equation such as (44) subject to arestrictive condition such as equation (45) is by Lagrange's method ofundetermined multipliers. Thus $\begin{matrix}{{\delta_{i} = {\delta_{i - 1}{\exp \left( \frac{\delta_{- 1} - \delta_{i - 2}}{\delta_{i - 1}} \right)}}};{i = {2\quad {to}\quad n}}} & (46)\end{matrix}$

[0284] The values of the parameters δ₁, δ₂, . . . δ_(n−1); λ₁, λ₂, . . ., λ_(n) and ψ_(n) are determined by trial-and-error as depicted by theflow chart of FIG. 13b. A computer code in “C” language is given inTABLE II for calculating the optimum (with respect to performance)partitioning ratios for a single photocell catalytic media of thepresent invention. Again, the procedure just described results in acatalytic media and reactor configuration that is optimal with respectto the DRE of the target species but not pressure drop across thecatalytic reactor.

[0285] TABLE III depicts the partitioning ratios for theoptimum-performance, single-cell, and multi-segmented media having up to7 partitions (calculated for exit DRE of 99.5%). TABLE IV depicts theextent of performance improvement expected in a range of DREs (varyingfrom 70 to 99.9999%) for optimum-performance multi-stage low- andhigh-flux media having up to non-equal states, where n denotes thenumber of single-cell partitions chosen. In many applications, it isdesirable to employ a media and reactor configuration that provides theleast amount of pressure drop albeit at somewhat reduced overall systemperformance. TABLE II ns=10 '# of stages/partitions a1guess=0.1 'initialestimate of a₁ ntrial=100 '# of iterations to determine a₁ j=2.5'exponent for rapid convergence, >2 nt=count(col(1)) 'enter % DREs incolumn 1 col(2)=1-col(1)/100 'δ_(f) values for n=1 to nt docell(3,n)=a1guess{circumflex over ( )}j for nn=1 to ntrial docell(ns+2.n)=cell(3.n) cell(ns+3.n)=cell(3.n) for i=4 to ns+1 docell(i.n)=((cell(3.n)){circumflex over( )}(1−1/j))*(exp(cell(i−1.n)/(cell(3.n)){circumflex over( )}(1−1/j))−1) cell(ns+2.n)=cell(ns+2.n)+cell(i,n) end forcell(ns+2.n)=-ln(cell(2.n))*(cell(3.n)){circumflex over( )}(1−1/j)−cell(ns+2.n) for ir=ns+1 to 3 docell(ir.n=(ln(cell(ir+1,n)/(cell(3.n)){circumflex over( )}(1−1/j)+1))*(cell(3.n)){circumflex over ( )}(1−1/j) end forcell(2*ns+5,n)=abs(cell(ns+3.n)-cell(3,n))/cell(3.n)*100 end forcell(3.n)=(cell(3.n)){circumflex over ( )}(1/j) cell(ns+3.n)=cell(3.n)cell(2*ns+6,n)=cell(3,n) for i2=4 to ns+2 docell(ns+i2.n)=exp(cell(ns+i2−1.n))−1cell(ns+3,n)=if(i2=4,cell(ns+3.n),cell(ns+3,n)+cell(ns+i2−1,n))cell(i2.n)=cell(ns+i2,n)/exp(cell(ns+3.n))cell(2*ns+6,n)=cell(2*ns+6,n)+cell(i2,n) end forcell(2*ns+3,n)=−ln(cell(2,n))/cell(2*ns+6,n)cell(2*ns+4,n)=(1−cell(2,n))/cell(2*ns+6,n)*100 for i3=2*ns+2 to ns+3 docell(i3.n)=cell(i3−ns,n)/cell(2*ns+6,n)*100 end forcell(2*ns+6,n)=100*cell(2,n) end for

[0286] TABLE III # of sta- ges. n 1✓L 1✓L 1✓L 1✓L 1✓L 1✓L 1✓L 1 1 20.6636 0.3364 3 0.4934 0.3291 0.1775 4 0.3962 0.2957 0.1989 0.1092 50.3245 0.2605 0.1978 0.1371 0.0801 6 0.2768 0.2316 0.1870 0.1432 0.10070.0606 7 0.2413 0.2077 0.1744 0.1415 0.1092 0.0778 0.0480

[0287] TABLE IV # of stages % Destruction & Removal Efficiency (DRE) n99.9999 99.999 99.99 99.9 99.5 99 90 85 80 75 70 1 1 1 1 1 1 1 1 1 1 1 12 4.029 3.572 3.1 2.612 2.259 2.103 1.566 1.469 1.399 1.344 1.299 36.275 5.398 4.513 3.621 2.994 2.724 1.834 1.681 1.573 1.49 1.423 4 7.7036.537 5.369 4.205 3.402 3.063 2.045 1.801 1.67 1.571 1.491 5 8.789 7.4246.061 4.703 3.765 3.365 2.089 1.878 1.732 1.622 1.533 6 9.528 8.02 6.5155.02 3.988 3.55 2.159 1.932 1.775 1.657 1.563 7 10.083 8.468 6.857 5.2584.156 3.689 2.211 1.972 1.807 1.683 1.584 8 10.514 8.816 7.124 5.4434.286 3.796 2.252 2.002 1.831 1.702 1.6 9 10.857 9.094 7.337 5.592 4.3913.882 2.283 2.026 1.85 1.718 1.613 10  11.137 9.321 7.511 5.713 4.4763.953 2.309 2.045 1.865 1.73 1.623 ∞ 13.816 11.513 9.211 6.915 5.3254.652 2.558 2.232 2.012 1.848 1.72

EXAMPLE 15

[0288] The analysis presented in EXAMPLE 14 is repeated with theobjective of minimizing the overall pressure drop instead of maximizingits performance. Again, the Lagrange's method of undeterminedmultipliers can be employed which results in a uniformly partitionedmedia configuration. In other words, a single-cell catalytic processhaving equipartitioned media stages, will have the lowest overallpressure drop than all the like ones but having unequal reaction stages.An analytical technique similar to that described in EXAMPLE 14 for thehigh-performance media and photoreactor design can be used also todetermine the performance (ψ_(n)) of a uniformly partitioned(equipartitioned) photocatalytic reactor as follows:

[0289] Consider the equipartitioned catalytic media of the photo-cell1400 depicted in FIG. 14a that comprises a longitudinal impermeableshell 1404 with inlet end 1402 and outlet end 1406 and a UV lamp 1409having protective sleeve 1408 coaxially mounted therein. The firstcatalytic media 1410 inside the shell has one end 1412 connected to theinlet 1402 of the impermeable shell 1404 and an opposite end 1416connected to the UV lamp sleeve 1408 at distance L/n. A second catalyticmedia 1420 has one end 1422 connected to inside the shell 1404 and anopposite end 1426 connected to the UV lamp sleeve 1408 at distance L/n,as well. The third catalytic media 1430 is connected similarly atdistance L/n as well as the n^(th) catalytic media 14n0, which is alsoconnected at distance L/n. The length of all partitioned media stagesare equal to one another. Each media segment forms a different stage(i.e. stage 1, stage 2, stage 3, . . . stage n). Fluid carryingcontaminant A flows into inlet end 1411 of the first media 1410 throughsides of first media to a space between the catalytic media 1410 and theimpermeable shell 1404 and then in a like manner into the other mediai.e. 1320, 1330, . . . , 13n0, respectively until it exits from theoutlet end 1406 of the impermeable shell 1404. Now, with reference toFIG. 14a, and noting that: λ₁=λ₂=. . . =λ₁=. . . =λ_(n)=l/n, write$\begin{matrix}{{\frac{\delta_{i}}{\delta_{i - 1}} = {\exp \quad \left( \frac{\ln \quad \delta_{f}}{n\quad \psi_{n,m}\delta_{i - 1}} \right)}};{1 = {1\quad {to}\quad {n.}}}} & (47)\end{matrix}$

[0290] Subject to following restrictions:

[0291] δ₀=1 and δ_(n)=δ_(f)

[0292] Sum both sides of equation (47) to get $\begin{matrix}{{\psi_{n} \equiv \frac{\ln \quad \delta_{f}}{{\ln \quad \delta_{1}} + {\sum\limits_{i = 2}^{n}{\delta_{i - 1}\ln \quad \frac{\delta_{i}}{\delta_{i - 1}}}}}}{Also}{{n\quad \psi_{n}} = \frac{\ln \quad \delta_{j}}{\ln \quad \delta_{1}}}{Then}} & \quad \\{{\delta_{i} = {\delta_{i - 1}\exp \quad \left( \frac{\ln \quad \delta_{1}}{\delta_{i - 1}} \right)}};{i = {2\quad {to}\quad {n.}}}} & (48)\end{matrix}$

[0293] The system of algebraic equations above can be solved bytrial-and-error according to the flow diagram of FIG. 14b. Equation (46)and (48) are the basis of all single-cell, multistage catalytic mediadesign and optimization. TABLE V depicts the expected performanceimprovement, ψ_(n), for n equally segmented single photocell catalyticmedia (up to 10 equal stages) for a range of exit DREs varying from 70to 99.9999%. The predicted performance improvement depicted above hasbeen experimentally verified for a number of multistage (n=1 to 4)stockings and a multi-component waste stream containing nitroglycerineand acetone. It should be noted that the values given in TABLES III, IVand V are equally valid for any other combination of target compounds,apparent quantum yield of disappearance at the onset and inletconcentrations as long as no strongly adsorbed surface species arepresent. When the contaminant stream contains compounds such asplasticizers (e.g. di-n-propyladipate, diethylphathalate) or othersimilar compounds, the surface adsorption effects must be morerigorously accounted for and do affect results derived above. TABLE V #of stages % Destruction & Removal Efficiency (DRE) n 99.9999 99.99999.99 99.9 99.5 99 90 85 80 75 70 1 1 1 1 1 1 1 1 1 1 1 1 2 3.713 3.3252.92 2.496 2.183 2.043 1.551 1.458 1.392 1.339 1.296 3 5.691 4.951 4.1963.424 2.872 2.631 1.814 1.668 1.564 1.484 1.419 4 7.033 6.042 5.04 4.0263.309 2.998 1.967 1.788 1.662 1.565 1.487 5 7.985 6.813 5.633 4.4443.609 3.25 2.067 1.865 1.724 1.617 1.53 6 8.693 7.385 6.071 4.752 3.8293.432 2.139 1.92 1.768 1.652 1.559 7 9.24 7.827 6.409 4.989 3.997 3.5722.192 1.96 1.8 1.678 1.581 8 9.675 8.178 6.678 5.176 4.129 3.681 2.2331.991 1.824 1.698 1.597 9 10.031 8.465 6.897 5.328 4.237 3.77 2.2652.016 1.844 1.714 1.61 10  10.326 8.703 7.079 5.455 4.326 3.844 2.2922.036 1.86 1.727 1.621 ∞ 13.816 11.513 9.211 6.915 5.325 4.652 2.5582.232 2.012 1.848 1.72

[0294] In a like manner, it can be shown that the results given byequation (46) and (48) will be applicable to the high-flux media andreactor configurations of this invention as well.

EXAMPLE 16

[0295] This EXANMPLE demonstrates the preferred embodiments of thepresent invention for designing high flux reactors. FIG. 14c depicts theequipartitioned, multistage high-flux media and reactor configuration ofthis invention that can be analyzed in a manner analogous to thelow-flux photosystem of FIG. 14a. FIG. 14c combines the multistageequipartitioned embodiments of FIG. 14a with the high-flux media andreactor configuration of FIG. 9b, where the multistage embodiment issubstituted for the single-stage fluidized bed media of FIG. 9b In FIG.14c, fluid carrying contaminant A flows in the direction of arrow A intothe rotating catalytic stages l, . . . , n−1, n from the dark side ofthe rotating media 1455, 1565 . . . 14n5. in a manner described in FIG.9b before. In FIG. 14c, high-flux multistage rotating fluidized bedreactor 1440 has rotating stages 1450, 1460 . . . , 14n0, where n equalsthe number of partitions or baskets, all rotating in unison aboutstationary lamp 30 b placed within the quartz sleeve 30 c, also rotatingin unison with the baskets. Fluid carrying contaminant A flows into theinlet port 21 and passes under the closed end 1452 of the basket 1450and through the round perforated side 1454 and through high-fluxcatalytic media 1455 (suspended in place by the combined but opposingaction of centrifugal outward acceleration of the media particles andinward acceleration due to aerodynamic drag forces on the mediaparticles) into inner lit space 1450 and out the circumferencial gapopening 1456 near lip 1453. After which the contaminant fluid streamsinto the second rotating stage/basket 1460 beneath the closed end 1462through perforated side 1464 through catalytic media 1465 into the innerlit space 1460 and out of the circumferencial gap opening 1466 next tolip 1463. Final contaminant flow streams through basket stage 14n0, in alike manner, having similar components 14n2, 14n4, 14n5, and out theexit port 14n6.

[0296] The multistage catalytic media and reactor design equationsdescribed in EXAMPLE 14 and 15 give the reactor performance in terms ofa normalized throughput (with respect to that of a simple, single-stagecatalytic media/reactor). The analytical results derived above and givenin TABLE V for an equipartitioned single-cell photoreactor having “n”identical catalytic media or reaction stages are also applicable to aphotosystem comprised of “n” identical series photocells. Results ofTABLE V imply that a system of n series photoreactors or a singlephotoreactor having n segmented stages shall perform progressivelybetter as the number of units in series or stages within a photocell, n,is increased. It is also clear from the discussion above that anoptimized photocell and media of this invention will deliver slightlyhigher DRE than a comparable one with the same number of equal stages(compare results of TABLE IV and V).

[0297] It can be appreciated that depending on the number of reactionstages chosen (ie. “n”), in certain applications, it may be better toaccept a slightly lower performance by segmenting the catalytic mediainto equal length partitions than design for optimum performance. Thisis so because the multistage cell pressure drop increases quickly as thenumber of reaction stages, n, is increased For the low-flux catalyticmedia (stocking) of the present work, the skin pressure drop can becalculated from Darcy's law for flow through porous media (i.e.ΔP_(l)=ku_(i)) as follows: $\begin{matrix}{\frac{\Delta \quad P_{n}}{\Delta \quad P_{1}} = {\psi_{n}{\sum\limits_{i = 1}^{n}\frac{1}{\lambda_{i}}}}} & (49)\end{matrix}$

[0298] In this equation ψ_(n) is given by equation (42) andλ_(l)=l_(i)/L, as before. The permeability factor, k, is primarily afunction of the type of fabric material or media used, weight and weavedensity, as well as the catalyst type and loadine density applied. For atypical low-flux media of the present invention such as super flannelfabric coated with Kemira, UNITI-908 TiO₂ at a loading density of about10% by weight of the fabric. k=0.075″ H₂O/(cm/s), approximately. FIG. 15depicts the trade-off between performance (i.e. high DREs due to largenumber of media stages, n, chosen) and the corresponding cell skinpressure drop.

[0299]FIG. 16 depicts the low-flux design of the double-stage catalyticstocking 1600. The double-stage stocking consists of two segmentspartitioned at approximately 66 and 34% of the total photocell length.This is critical for achieving optimum conversion at a designated DRE of99.5%. Different partitioning proportions must be used if the target DREdiffers from the value above. The new partitioning ratios can be derivedusing the computer program given in TABLE III.

[0300] Referring to FIG. 16, double-stage stocking embodiment 1600includes inlet flange 1602 having an interior opening. A hollowimpermeable wall shell 1610 (fabricated from any suitable material suchas DuPont's TYVEK^(R) for flexible media or hard metallic tube if rigidshell design) has one end 1612 tie wrap connected to the opening ininlet flange 1602 and a second end 1613 connected to one end 1627 of alast stage catalytic media 1628 (prepared as previously described).Opposite end 1626 of last stage catalytic media is tie wrapped to aperimeter edge of an exit flange 1604. Along a central axis of shell1610 is a UV lamp 1630 placed within a quartz or ed silica sleeve 1629.One of the lamp ends 1632 lies adjacent to the close end 1633 of thequartz sleeve 1629 which is adjacent an opening 1601 in inlet flange1602. The opposite end 1634 of the lamp 1630 connects to power supplyleads 1635 that make the connection via the open end 1603 of the quartzsleeve 1629. The open end 1603 of the quartz sleeve 1629 is held inplace within the opening of exit flange 1604 through which the quartzcooling dip tube 1637 services the UV lamp 1630 within the quartz sleeve1629.

[0301] A first stage permeable catalytic media 1622 has an inlet end1621 tie wrapped 1612 around passageway opening 1601 of inlet flange1602, and a second end 1623 tied to a first mid-portion 1631 of quartzsleeve 1629.

[0302] A last stage permeable media 1628 has an inlet end 1624 connectedto the exit/second rim 1613 of shell 1610, and a second end 1626 tiewrapped to a perimeter edge of an exit flange 1604.

[0303] Referring to FIG. 16, contaminated stream A flows into inletopening 1601 of inlet flange 1602 in the direction of arrow E1, andflows over quartz sleeve closed end 1633 and through side walls of firststage permeable media 1622 in the direction of arrow E2 to the airspacebetween first media 1622 and interior walls of impermeable shell 1610.Stream A then flows in the direction of arrow E4 through the side wallsof last stage permeable media 1628 and out of the double-stage photocellof the subject invention in the direction of arrow E5.

EXAMPLE 17

[0304] This Example demonstrates the application of a two-stagephotocatalytic stocking (DSPCS). A DSPCS was fabricated and tested usingthe photoreactor of EXAMPLE 7. Again, the reagent solution usedcontained 5% by weight nitroglycerin in acetone as in EXAMPLE 13. Thecarrier gas was air heated to approximately 95° C. and flowing at 15.5SCFM (approximately 20.2 ACFM) through the mixing chamber 158 (FIG. 11b)and then into photocatalytic reactor 110 (FIG. 11b) of EXAMPLE 7.Concentration of NG in the gas-phase was approximately 9.6 ppmv. Again,the stocking was cotton flannel having an OD of about 3.8 inches. Thestocking had 2 stages with proportions for stage 1, and 2 beingapproximately 67, and 33 percent of the total stocking length,respectively. The nitroglycerin DRE was determined at about 98.3%(99.99% at the exit). The average nitroglycerin residence time wascalculated to be about 36 ms.

[0305]FIG. 17 depicts the low-flux design of the triple-stage catalyticstocking 1700. The 3-stage stocking consists of three segmentspartitioned at approximately 49, 33 and 18% of the total photocelllength. This is critical for achieving optimum conversion at adesignated DRE of 99.5%. Different partitioning proportions must be usedif the target DRE differs from the value above. The new partitioningratios can be derived using the computer program given in TABLE III.

[0306] Referring to FIG. 17, triple stage stocking embodiment 1700includes inlet flange 1702 having an interior opening. A hollowimpermeable wall shell 1710 (made from any suitable material such asDuPont's TYVEK if flexible design or hard metallic shell. e.g. aluminumor steel, if rigid design) has one end 1712 tie wrap connected to theopening in inlet flange 1702 and a second end 1714 connected to one end1727 of a last stage catalytic media 1728 (prepared as previouslydescribed). Opposite end of the last stage catalytic media is tiewrapped to a perimeter edge of an exit flange 1704. Along central axisof shell 1710 is a UV lamp 1730 placed within a quartz or fused silicasleeve 1729. One of the lamp ends 1732 lies adjacent to the close end1733 of the quartz sleeve 1729 which is adjacent an opening 1701 ininlet flange 1702. The opposite end 1734 of the lamp 1730 connects topower supply leads 1735 that make the connection via the open end 1703of the quartz sleeve 1729. The open end 1703 of the quartz sleeve 1729is held in place within the opening of exit flange 1704 through whichthe quartz cooling dip tube 1737 services the UV lamp 1730 within thequartz sleeve 1729.

[0307] A first stage permeable catalytic media 1722 has an inlet end1721 tie wrapped 1712 around passageway opening 1701 of inlet flange1702, and a second end 1723 tied to a first mid-portion 1731 of quartzsleeve 1729.

[0308] A second stage permeable media 1725 has an inlet end 1724connected to an interior mid-wall portion 1713 of shell 1710, and asecond end 1726 tie wrapped to a second mid-portion 1733 along thequartz sleeve 1729.

[0309] A last stage permeable media 1728 has an inlet end 1727 connectedto the exit/second rim 1714 of shell 1710, and a second end 1750 tiewrapped to a perimeter edge of an exit flange 1704.

[0310] Referring to FIG. 17, contaminated stream A flows into inletopening 1701 of inlet flange 1702 in the direction of arrow F1, andflows over quartz sleeve closed end 1733 and through side walls of firststage permeable media 1722 in the direction of arrow F2 to the airspacebetween first media 1722 and interior walls of impermeable shell 1710.Stream A flows in the direction of arrow F3 into inlet end 1713 ofsecond stage permeable media 1725 and in the direction of arrow F4through second stage media side walls 1725 and to the airspace betweenthe second media 1725 and interior walls of impermeable shell 1710.Stream A then flows in the direction of arrow F5 through the side wallsof last stage permeable media 1728 and out of the 3-stage photocell ofthe subject invention in the direction of arrow F6.

EXAMPLE 18

[0311] This EXAMPLE relates to test results for a three-stagephotocatalytic stocking (TSPCS). The experimental conditions andprocedure for this test were essentially identical to that described inEXAMPLES 13 and 17 except that air was heated to about 90° C. andmetered at 29.95 SCFM (38.2 ACFM) through the mixing chamber 158 (FIG.11b) and into the photoreactor 110 (FIG. 11b) of EXAMPLE 7.Concentration of nitroglycerin in the gas-phase was 9.3 ppmv. Thematerial of the stocking was cotton flannel (see EXAMPLE 13 & 17),having an OD of 3.75 inches. The stocking had 3 stages The active lengthof stage 1, 2 and 3 were approximately 49, 33, and 18 percent of thetotal TSPCS length, respectively. Total volume of NG/acetone solutioninjected was approximately 160.1 ml. Total experiment run time was 81minutes. The NG DREs varied between 75% and 87% (corresponding to exitDRE of 88% and 100%, respectively). The average NG residence time wascalculated to be approximately 15 ms.

EXAMPLE 19

[0312] This EXAMPLE demonstrates the application of a 4-stage(equipartitioned) photocatalytic stocking (QSPCS). All experimentalconditions and procedure for this case were essentially same as EXAMPLE18 except that air was heated to about 95° C. and flowing at 40 SCFM(approximately 52 ACFM) through the mixing chamber 158 (FIG. 11b) andinto the photoreactor 110 (FIG. 11b) of EXAMPLE 7. Concentration of NGin the gas-phase was about 9.55 ppmv. The material of the stocking wassame as the EXAMPLES 13, 17 and 18 but having an OD of approximately3.75 inches. Average UV light intensity on the inner surface of theQSPCS (at mid length) was measured (using ILC radiometer) to be about2.06 mW/cm² (for λ=254 nm). NG DREs varied between 68.4% and 81.5%(corresponding to exit DRE of 77% and 90%, respectively). Total NGresidence time within the QSPCS was calculated to be approximately 10.8ms.

[0313] The predicted values (from equations 39-48) for Q_(n) are plottedagainst the experimental values (from data of EXAMPLES 13, and 16 to 18)in FIG. 18. It can be seen that a good agreement is obtained between thepredicted and measured values of Q_(n). In general, the agreementbetween the predicted values and experimental data improves as thenumber of reaction stages is increased. There is also a largeuncertainty associated with some of data as evident by the size of theerror bars on the graph. Now, decoupling at module-level will bedisclosed.

[0314] The benefits accrued from partitioning the catalytic stockingscan be also realized by series arrangement of the single-cell reactorseach containing a single-stage photocatalytic stocking. Therefore, theoverall performance of a catalytic system comprised of many single-cellunits will increase substantially by arranging all the unit cells in thesystem in series with each other. Again, the penalty to be paid forseries arrangement of the photocells is the increased pressure dropthrough the unit. It is now understood that an increased photocatalyticsystem performance (i.e. higher target DRES) can result from either orcombination of the following three design approaches:

[0315] 1—Single-cell implementation of the multistage catalytic media

[0316] 2—Module-level arrangement of the single-cell reactors, in serieswith each other.

[0317] 3—Unit-level arrangement of the individual sub-units or modulesin series, together.

[0318] Clearly, as far as the unit-level design is concerned, the unitcells or single photocells of the photosystem can be arranged in anumber of different ways. For example, it is possible to arrange all ofthe photocells in parallel. In this way, the incoming flow dividesequally amongst all individual single-cell photoreactors (i.e.photocells or unit cells). Alternatively, the unit cells can be dividedinto smaller groups or banks that are plumbed to one another in seriesto form a cluster of parallel branches each containing two or more unitcells, in series. It should be clear from discussions above that theprocess DRE is a function of both Oo of the target contaminant and themanner in which the individual photoreactors (photocells or sub-units)and catalytic media within each photoreactor has been configured.

[0319] Now, the criteria for the design and engineering of complexphotosystems that combine the module-level decoupling with the singlecell-level (media-level) partitioning to achieve optimum photosystemperformance are disclosed.

EXAMPLE 20

[0320] This EXAMPLE describes the preferred embodiments of the presentinvention in the context of designing a double-bank, equipartitionedmultistage series reactors. FIG. 19a depicts the configuration of onepreferred embodiment of the present invention that has been reduced topractice as a full-scale photocatalytic pollution control unit (PPCU).FIG. 19a combines two equipartitioned multistage embodiments 1900 (BankA) and 1900′ (Bank B) in series. Depending on the volume of the flow tobe treated by the process, concentration of the target species andultimate DRE desired. Bank A and B may comprise one or several likephotocells connected in parallel to each other. Also, Bank A 1900 canhave n stages (at media-level) while Bank B has m stages (atmedia-level), where n can be less than, equal to or greater than mn, aslater described in reference to FIG. 20. Now, with reference to FIG.19a, for two equipartitioned multistage series photoreactors, for theupstream photocell or Bank A (i.e. 1900) having “n” equal stages, write${\delta_{i} = {\delta_{i - 1}\exp \quad \left( \frac{\ln \quad \delta_{f}}{n\quad \psi_{n,m}\delta_{i - 1}} \right)}};{i = {1\quad {to}\quad {n.}}}$

[0321] For the downstream photoreactor (Bank B 1900′) having a mediawith “m” equal stages, write${\delta_{i} = {\delta_{i - 1}{\exp \left( \frac{\ln \quad \delta_{f}}{n\quad \psi_{n,m}\delta_{i - 1}} \right)}}};{i = {n + {1\quad {to}\quad n} + {m.}}}$

[0322] Subject to constraints:

[0323] δ₀=1; δ_(n)=δ₀ and δ_(n,m)=δ_(f),

[0324] Then $\begin{matrix}{{{\ln \quad \delta_{1}} = \frac{\ln \quad \delta_{f}}{n\quad \psi_{n,m}}}{or}{\eta_{n,m} = {{- \frac{\ln \quad \delta_{f}}{\psi_{n,m}}} = {{- n}\quad \ln \quad \delta_{1}}}}{and}} & \quad \\\left\{ \begin{matrix}{{\delta_{i} = {\delta_{i - 1}{\exp \left( \frac{\ln \quad \delta_{1}}{\delta_{i - 1}} \right)}}};{i = {2\quad {to}\quad {n.}}}} \\{{\delta_{j} = {\delta_{j - 1}\exp \quad \left( \frac{n\quad \ln \quad \delta_{1}}{m\quad \delta_{j - 1}} \right)}};{j = {n + {1\quad {to}\quad n} + {m.}}}}\end{matrix} \right. & (50)\end{matrix}$

[0325] The system of algebraic equations above can be solved iterativelyaccording to the flow chart shown in FIG. 19b.

[0326] In a like manner, FIG. 19c depicts the configuration of yetanother embodiment of the present invention. FIG. 19c combines twomultistage embodiments 1300 (Bank A) and 1300′ (Bank B) in series.Again, Bank A and B may comprise one or several like photocellsconnected in parallel to each other. Also, Bank A 1300 can have nunequally divided stages (at media-level) while Bank B has m unequallydivided stages (at media-level), where n can be less than, equal orgreater than m, as discussed below.

[0327] The most desirable configuration for a given application dependson the exit DRE required maximum pressure drop allowed, economic, andother considerations. Furthermore, the number of partitions at the cellor media levels as well as the level of partitioning chosen within eachbank greatly affects the photosystem performance. The optimizationcalculations have been carried out for a number of configurationsinvolving different combination of the partitioning numbers n and m forphotosystems of FIG. 19a and 19 c, with NG as the primary targetcontaminant at the inlet concentration of 10 ppmv. Typical results aregiven in FIG. 20. It can be seen that combining parallel and seriesinterconnects results in a substantial process efficiency improvement.Results of FIG. 20 indicate that the photosystem efficiency is higherwhen the number of partitioned media in the downstream bank in themodule is larger than that in the upstream bank of the series. In otherwords, if nm denotes n stage media implementation at the upstream bankof the module and m stage media implementation at the downstream bank inthe module, then nm arrangement will give considerably higherphotosystem performance than mn arrangement, where n<m. It isinteresting to note that even though nm arrangement gives higherphotosystem performance than mn arrangement (when n<m), bothconfigurations will result in exactly the same pressure drop across theunit.

[0328] It can be appreciated that a large number of combinationsincorporating the decoupling concept at the media-, module- andunit-levels are possible and not all can be mentioned and discussedhere. Nonetheless, the methodologies developed in previous sections anddescribed in many EXAMPLES given above are sufficient to allow exactcalculation of the results and benefits derived from any otherarrangement not covered in this disclosure.

EXAMPLE 21

[0329] This EXAMPLE describes a full-scale system design based on theconcepts disclosed here that is reduced into practice by the subjectinventor. This EXAMPLE demonstrates the application of a partiallydecoupled photocatalytic pollution control unit (PPCU) based on amultistage design implemented at all component levels, i.e. at media-,module and unit-levels. With reference to FIG. 21a and 21 b, thefull-scale low-flux PPCU consists of two sub-units or modules 2100 and2110 (FIG. 21a) or 2120 and 2130 (FIG. 21b), plumbed together, inparallel to each other. FIG. 21a shows a two-by-two series-parallelarrangement of equalpartitioned multistage media (stockings)implementation. In FIG. 21a, fluid containing contaminant splits betweentwo identical sub-units or modules 2100 and 2110. Each sub-unit ormodule consists of 32 photocells clustered together (not shown in FIG.21a) in two banks of 16 photocells each. Thus. each module has two banksand wherein each branch comprised of two photocells in series (1900 and1900′ in module 2100 and 1900″ and 1900′″ in module 2110). In otherwords, PPCU is arranged so that each of the two parallel modules has twobanks of 16 branched photocells each or 16 parallel branches (not shownin FlG. 21 a). In this arrangement, the incoming flow into each sub-unitor module splits into parallel streams (branches) and passes through 16photocells of the first bank (1900 and 1900″) before entering the secondbank of 16 parallel photocells (1900′ and 1900′″). FIG. 21b depicts aconfiguration similar to FIG. 21a except that the partitioning at thecell-level comprises unequal multistage media segmentation. Inprinciple, it is possible to have multistage, cell-level segmentation ofboth equal and unequal type in one unit or a module. In practice. otherconsiderations (e.g. cost inventory, maintenance and service of the unitetc.) are likely to limit the type and number of cell-level,module-level and unit-level multi-staging and rearrangements. FIG. 21a,with double or triple equipartitioned multistage stockings presents themost likely and practical PPCU, configuration that can be implemented.It is important to note that the PPCU of FIG. 21a and 21 b was designedand intended to use multistage stockings. The PPCU light chamber wasintended to be simple design and thus no inlet manifold (flowdistributor) was envisioned to be required. This is justified becausethe use of multistage stockings with the unit mitigates the effect offlow non-uniformity normally present with the use of single-stagestockings.

EXAMPLE 22

[0330] This EXAMPLE demonstrates the preferred embodiments of thepresent invention for designing high-flux photocatalytic,thermocatalytic or combined photo- and thermocatalytic reactors andmedia. The general layout of the multistage high-flux catalytic mediaand reactor configuration of the present invention at the single-celllevel has already been described in FIG. 9b. Just as the low-flux systembenefits from the module-level and unit-level decoupling, the high-fluxsystem can also realize considerable performance boost by the seriesarrangement of the single-cell reactors. In other words, the overallperformance of a high-flux catalytic system comprised of manysingle-cell units will increase substantially by arranging all the unitcells in the system in series with each other. Again, the penalty to bepaid for series arrangement of the photocells is the increased pressuredrop through the unit. In short, increased high-flux system performancecan accrue from decoupling at the cell or media-level, module orbank-level and unit-level implementation and optimization.

[0331] The preferred embodiments and design of the high-flux catalyticmedia of the present invention is now disclosed with reference to FIG.22. FIG. 22 depicts a 2-stage high-flux version of the low-fluxfull-scale unit of EXAMPLE 17, described before. The high-flux catalyticmedia 2200 & 2205 useful for the practice of this invention are from thegroup of dual function catalysts of the Type III (e.g. transparentco-gelled SiO₂/TiO₂ aerogels) and Type V (e.g. cation modified zeolitesand noble or base metal supported titania). These moderate temperaturecatalytic media (approximately 200-400° C.) are most suited for thehigh-flux thermocatalytic and photocatalytic process engineering andreactor design applications.

[0332] The high-flux reactor design also follows the same guidelinesdescribed before for the low-flux reactor design and analysis. Onepreferred embodiment of the present invention for the high-flux reactorconfiguration that readily satisfies the decoupling requirements isrotating fluidized bed reactor 2210. FIG. 22 depicts one preferredembodiment of this Invention. The unit comprises two rotating fluidizedbed reactors 2215 & 2220, in tandem, which rotate in the direction ofarrow R1 within a plenum vessel 2210. The baskets 2225 & 2230 rotate athigh speed to hold catalyst particles within by the centrifugal action.The contaminant stream enters via perforated basket wall and distributor2240 & 2245. The contaminated flow 2250 enters radially and exitsaxially, at the top 2255 and bottom 2260 of basket 2225 and 2230.High-flux lamps 2270 & 2275 (e.g. medium pressure mercury lamps such asVoltarc Tubes. Inc. UV LUX series lamps) are placed into thefused-silica sleeves 2280 & 2285 located at the middle, along the axisof the reactor, see FIG. 22. Two identical reactors 2225 & 2230 inseries provide higher combined process efficiency due to partialdecoupling effect, discussed before. The rotational speed of the basketscan be varied automatically to control catalyst carry over. This isparticularly important in the case of transition metal aerogels as thebed material. Catalyst particles can be fed into the reactors throughthe injection tubes 2290 & 2295. The rotating beds 2230 & 2240 can beoperated in either horizontal or vertical configuration. The type ofcatalytic media used in each reactor can be the same or differentdepending on the type of waste stream to be treated. Means can beprovided for easy loading and removal of the bed materials. It ispossible to run the centrifugal reactor under either fluidizing orpacked bed conditions. The reactor parameters can be readily modified tomeet the requirements of the treatment process.

[0333] It is to be noted that the contaminated stream that can betreated with the methods of the subject invention can be a fluid such asbut not limited to air, gas, liquid, combination thereof and the like.As noted before, the contaminated stream can contain solid andparticulate matter.

[0334] Although some preferred embodiments show the direction of thestream containing contaminants in one direction, the invention caneffectively operate with the contaminant flow through the oppositedirection, i.e. through inlet end to outlet end and vice versa.

[0335] It is to be understood that the disclosure above is meant to berepresentative of the techniques and methods most useful to the practiceof this invention. Since many modifications to the main embodiments ofthe invention can be made without departing from the spirit and scope ofthe invention, it is intended that all matter contained in the abovedescription and shown in the accompanying drawings shall be interpretedas illustrative and not in a limiting sense.

[0336] It is also to be understood that the following claims areintended to cover all generic and specific features of the inventionherein described and all statements of the scope of the invention which,as a matter of language, might be said to fall therebetween.Particularly, it is to be understood that in said claims, features,ingredients or compounds recited in the singular are intended to includecompatible mixtures of such ingredients wherever the sense permits. Weclaim:

1. An apparatus for low flux photocatalytic pollution controlcomprising: a low flux longitudinal light source having a first end anda second end; a first stage photocatalytic reactor having a first lengthabout the first end of the light source, for converting a first portionof a target pollutant to a pre-determined level of destruction andremoval efficiency (DRE) by passing the target pollutant through thefirst stage photocatalytic reactor, and a last stage photocatalyticreactor having a second length about the second end of the light sourcefor converting a last portion of the target pollutant passing throughthe second stage photocatalytic reactor to a selected final DRE level.2. The apparatus for low flux photocatalytic pollution control of claim1 , wherein the low flux longitudinal light source includes:Low-pressure mercury vapor lamp.
 3. The apparatus for low fluxphotocatalytic pollution control of claim 1 , wherein the low fluxlongitudinal light source includes: a medium to high-pressure mercuryvapor lamp.
 4. The apparatus for low flux photocatalytic pollutioncontrol of claim 1 , wherein the first stage reactor and the last stagereactor each comprise: an identical catalytic material.
 5. The apparatusfor low flux photocatalytic pollution control of claim 1 , wherein thefirst stage reactor and the last stage reactor each comprise: adifferent catalytic material.
 6. The apparatus for low fluxphotocatalytic pollution control of claim 4 , wherein the photocatalyticmaterial includes: an elemental composition of Carbon, Oxygen, Hydrogenand Titanium.
 7. The apparatus for low flux photocatalytic pollutioncontrol of claim 6 , wherein the composition of the catalytic mediaincludes: approximately 30% to approximately 50% by weight Carbon;approximately 40% to approximately 60% by weight Oxygen; approximately4% to approximately 10% by weight hydrogen; and approximately 0.1% toapproximately 20% by weight Titanium.
 8. The apparatus for low fluxphotocatalytic pollution control of claim 7 , wherein the compositionthe catalytic media includes: approximately 40% to approximately 45% byweight Carbon; approximately 47.5% to approximately 50% by weightOxygen; approximately 5.5% to approximately 6% by weight Hydrogen; andapproximately 1.5% to approximately 5% by weight Titanium.
 9. Theapparatus for low flux photocatalytic pollution control of claim 4 ,wherein the photocatalytic material includes: an elemental compositionof Carbon, Oxygen, Hydrogen, Cadmium and Sulfur.
 10. The apparatus forlow flux photocatalytic pollution control of claim 9 , wherein thecomposition includes: approximately 34% to approximately 45% by weightCarbon; approximately 38% to approximately 50% by weight Oxygen;approximately 4.75% to approximately 6.25% by weight Hydrogen;approximately 7% to approximately 17.1% by weight Cadmium; andapproximately 0.2% to approximately 5% by weight Sulfur.
 11. Theapparatus for low flux photocatalytic pollution control of claim 1 ,wherein the first stage reactor includes: an outer impermeable hollowshell with an inlet end about the first end of the lght source, and anoutlet end before the second end of the light source, a first permeablephotocatalytic jacket inside the outer impermeable shell having a firstend connected to the inlet end of the shell and a second end connectedto a first location on the lamp source, and wherein the last stagereactor includes: a last permeable photocatalytic jacket having a firstend connected to the outlet end of the outer impermeable shell and asecond end connected adjacent the second end of the light source,wherein fluid flows into the first end of the first-jacket throughpermeable photocatalytic sidewalls of the first jacket into a spacebetween the first jacket and the outer impermeable shell, into theinterior of the last photocatalytic jacket and outward through permeablephotocatalytic sidewalls of the last jacket adjacent to the second endof the light source.
 12. The apparatus for low flux photocatalyticpollution control of claim 1 , comprising: a second stage photocatalyticreactor between the first stage photocatalytic reactor and the laststage photocatalytic reactor.
 13. The apparatus for low fluxphotocatalytic pollution control of claim 12 , wherein the first stagereactor includes: an outer impermeable hollow shell with an inlet endabout the first end of the light source, and an outlet end before thesecond end of the light source, and a first permeable photocatalyticjacket inside the outer impermeable shell having a first end connectedto the inlet end of the shell and a second end connected to a firstlocation on the light source, wherein the second stage reactor includes:a second permeable photocatalytic-jacket inside the impermeable shellhaving a first end connected to the shell adjacent to the second end ofthe first permeable photocatalytic jacket, and second end connected to asecond location on the light source between the first location and thesecond end of the light source, and wherein the last stage reactorincludes: a last permeable photocatalytic jacket having a first endconnected to the outlet end of the outer impermeable shell and a secondend connected adjacent the second end of the light source, wherein fluidflows into the first end of the first jacket and passes throughpermeable photocatalytic sidewalls of the first jacket into a spacebetween the first jacket and the outer impermeable shell, into the firstend of the second jacket, through permeable photocatalytic sidewalls ofthe second jacket into the space between the second jacket and the outerimpermeable shell, into the interior of the last photocatalytic jacketand outward though permeable photocatalytic sidewalls of the last jacketadjacent the second end of the light source.
 14. The apparatus for lowflux photocatalytic pollution control of claim 12 , further comprising:a third stage photocatalytic reactor between the second stagephotocatalytic reactor and the last stage photocatalytic reactor. 15.The apparatus for low flux photocatalytic pollution control of claim 14, wherein the first stage reactor includes: an outer impermeable hollowshell with an inlet end about the first end of the light source, and anoutlet end before the second end of the light source, and a firstpermeable photocatalytic jacket inside the outer impermeable shellhaving a first end connected to the inlet end of the outer impermeableshell and a second end connected to a first location on the lightsource, wherein the second stage reactor includes: a second permeablephotocatalytic jacket inside the outer impermeable shell having a firstend connected to the shell adjacent to the second end of the firstpermeable photocatalytic jacket, and second end connected to a secondlocation on the light source between the first location and the secondend of the light source, wherein the third stage reactor includes: athird permeable photocatalytic jacket inside the outer impermeable shellhaving a first end connected to the outer impermeable shell adjacent thesecond end of the second permeable photocatalytic jacket, and a secondend connected to a third location on the light source between the secondlocation and the second end of the light source, and wherein the laststage reactor includes: a last permeable photocatalytic jacket having afirst end connected to the outlet end of the outer impermeable shell anda second end connected adjacent the second end of the light source,wherein fluid flows into the first end of the first jacket and passesthrough photocatalytic sidewalls of the first jacket into a spacebetween the first jacket and the outer impermeable shell, into the firstend of the second jacket, through photocatalytic sidewalls of the secondjacket into the space between the second jacket and the outerimpermeable shell, into the first end of the third jacket, throughphotocatalytic sidewalls of the third jacket into the space between thethird jacket and the outer impermeable shell, into the interior of thelast photocatalytic jacket and outward through photocatalytic sidewallsof the last jacket adjacent to the second end of the light source. 16.The apparatus for low flux photocatalytic pollution control of claim 1 ,wherein the first stage reactor and the last stage reactor each haveunequal lengths.
 17. The apparatus for low flux photocatalytic pollutioncontrol of claim 16 , wherein the first stage reactor length is greaterthan the second stage reactor length.
 18. The apparatus for low fluxphotocatalytic pollution control of claim 1 , wherein the targetpollutant is chosen from at least one of: alcohols, ketons, aldehydes,carboxylic acids, nitrate esters, arnnes, halogenated compounds,plasticizers, hydrocarbons, terpenic compounds, nitrogen oxides, andsulfur gases.
 19. The apparatus for low flux photocatalytic pollutioncontrol of claim 1 , wherein the first stage reactor and the last stagereactor each have equal lengths.
 20. The apparatus for low fluxphotocatalytic pollution control of claim 1 , wherein the first stagereactor includes: a first outer impermeable hollow shell with an inletend about a first end of a first light source, and an outlet endadjacent a second end of the first light source. a first permeablephotocatalytic jacket inside the first outer impermeable shell having afirst end connected to the inlet end of the first impermeable shell anda second end connected to a first location on the first light source,and wherein the last stage reactor includes: a last outer impermeablehollow shell with an inlet end about a first end of a last light source,and an outlet end adjacent a second end of the last light source, a lastpermeable photocatalytic jacket inside the last outer impermeable shellhaving a first end connected to the inlet end of the last outerimpermeable shell and a second end connected to a first location on thelast light source, the first stage reactor in series to the last stagereactor, and wherein fluid flows into the first end of the first jacketthrough photocatalytic sidewalls of the first jacket in a space betweenthe first jacket and the first outer impermeable shell, into the firstend of the last jacket through photocatalytic sidewalls of the lastjacket into a space between the last jacket and the last outerimpermeable shell and outward therefrom.
 21. The apparatus for low fluxphotocatalytic pollution control of claim 20 , further comprising: asecond stage photocatalytic reactor between the first stagephotocatalytic reactor and the last stage photocatalytic reactor. 22.The apparatus for low flux photocatalytic pollution control of claim 21, wherein the first stage reactor includes: a first outer impermeablehollow shell with an inlet end about a first end of a first lightsource, and an outlet end adjacent a second end of the first lightsource, a first permeable photocatalytic jacket inside the first outerimpermeable shell having a first end connected to the inlet end of thefirst impermeable shell and a second end connected to a first locationon the first light source, and wherein the second stage reactorincludes: a second outer impermeable hollow shell with an inlet endabout a first end of a second light source, and an outlet end adjacent asecond end of the second light source, a second permeable photocatalyticjacket inside the second outer impermeable shell having a first endconnected to the inlet end of the second impermeable shell and a secondend connected to a first location on the second light source, andwherein the last stage reactor includes: a last outer impermeable hollowshell with an inlet end about a first end of a last light source, and anoutlet end adjacent a second end of the last light source, a lastpermeable photocatalytic jacket inside the last outer impermeable shellhaving a first end connected to the inlet end of the last outerimpermeable shell and a second end connected to a first location on thelast light source, the first stage reactor in series to the second stagereactor and the last stage reactor, and wherein fluid flows into thefirst end of the first jacket through photocatalytic sidewalls of thefirst jacket into a space between the first jacket and the first outerimpermeable shell, into the first end of the second jacket throughphotocatalytic sidewalls of the second jacket into a space between thesecond jacket and the second outer impermeable shell, into the first endof the last jacket through photocatalytic sidewalls of the last jacketinto a space between the last jacket and the last outer impermeableshell, and outward therefrom.
 23. The apparatus for low fluxphotocatalytic pollution control of claim 22 , further comprising: athird stage photocatalytic reactor between the second stagephotocatalytic reactor and the last stage photocatalytic reactor. 24.The apparatus for low flux photocatalytic pollution control of claim 23, wherein the first stage reactor includes: a first outer impermeablehollow shell with an inlet end about a first end of a first lightsource, and an outlet end adjacent a second end of the first lightsource, a first permeable photocatalytic jacket inside the first outerimpermeable shell having a first end connected to the inlet end of thefirst impermeable shell and a second end connected to a first locationon the first light source, and wherein the second stage reactorincludes: a second outer impermeable hollow shell with an inlet endabout a first end of a second light source, and an outlet end adjacent asecond end of the second light source, a second permeable photocatalyticjacket inside the second outer impermeable shell having a first endconnected to the inlet end of the second impermeable shell and a secondend connected to a first location on the second light source, andwherein the third stage reactor includes: a third outer impermeablehollow shell with an inlet end about a first end of a third lamp light,and an outlet end adjacent a second end of the third light source, athird permeable photocatalytic jacket inside the third outer impermeableshell having a first end connected to the inlet end of the thirdimpermeable shell and a second end connected to a first location on thethird light source, and wherein the last stage reactor includes: a lastouter impermeable hollow shell with an inlet end about a first end of alast light source, and an outlet end adjacent a second end of the lastlight source, a last permeable photocatalytic jacket inside the lastouter impermeable shell having a first end connected to the inlet end ofthe last outer impermeable shell and a second end connected to a firstlocation on the last light source, the first stage reactor in series tothe second stage reactor and the third stage reactor and the last stagereactor, and wherein fluid flows into the first end of the first jacketthrough photocatalytic sidewalls of the first jacket into a spacebetween the first jacket and the first outer impermeable shell, into thefirst end of the second jacket through photocatalytic sidewalls of thesecond jacket into a space between the second jacket and the secondouter impermeable shell, into the first end of the third jacket throughphotocatalytic sidewalls of the third jacket into a space between thethird jacket and the third outer impermeable shell, into the first endof the last jacket through photocatalytic sidewalls of the last jacketinto a space between the last jacket and the last outer impermeableshell, and outward therefrom.
 25. An apparatus for low fluxphotocatalytic pollution control comprising: first low flux longitudinallamps positioned parallel to each other; last low flux longitudinallamps positioned parallel to each other, and in series with the firstlow flux longitudinal lamps; first stage photocatalytic reactors,positioned parallel to each other, each of the first stagephotocatalytic reactors housing each of the first stage flow fluxlongitudinal lamps, wherein the first stage photocatalytic reactorsconverts a first portion of a target pollutant passing therethrough; anda last stage photocatalytic reactors, positioned parallel to each other,each of the last stage photocatalytic reactors including each of thelast stage low flux longitudinal lamps, wherein the last stagephotocatalytic reactors converting a last portion of the targetpollutants passing through the last stage photocatalytic reactors to aselected final DRE level.
 26. The apparatus for low flux photocatalyticpollution control of claim 25 , wherein the first stage reactors and thesecond stage reactors each include: approximately 2 to approximately 32lamps.
 27. The apparatus for low flux photocatalytic pollution controlof claim 25 , wherein the first stage reactors include: a single firstouter impermeable hollow shell with inlet ends about first ends of thefirst parallel lamps and outlet ends adjacent second ends of the firstparallel lamps; first permeable photocatalytic jackets inside the firstouter permeable hollow shell, each of the jackets having first endsconnected to the inlet ends of the first shell and second ends connectedto the outlet ends of the first shell; and wherein the last stagereactors include: a single last outer impermeable hollow shell withinlet ends about first ends of the last parallel lamps, and outlet endsadjacent second ends of the last parallel lamps; and last permeablephotocatalytic jackets inside the last outer impermeable hollow shell,each of the last jackets having first ends connected to the inlet endsof the last shell and second ends connected to the outlet ends of thelast hollow shell, wherein fluid flows into the first ends of the firstjackets adjacent the first ends of the first lamps and out through thepermeable photocatalytic sidewalls of the first jackets surrounding thefirst lamps into a space between the first jackets and the first outerimpermeable shell, and through an interconnect joining an exit port ofthe first shell to an inlet port of the last shell and into each of thelast photocatalytic jackets surrounding the last lamps and outwardthrough permeable photocatalytic sidewalls of the last jackets and intoa space between the last jackets and the last outer impermeable shelland out of the pollution control apparatus through an exit port of thelast hollow shell.
 28. The apparatus for low flux photocatalyticpollution control of claim 25 , wherein the length of each of the firststage reactors and each of the last stage reactors are equal to oneanother.
 29. The apparatus for low flux photocatalytic pollution controlof claim 25 , wherein the length of each of the first stage reactors andeach of the last stage reactors are unequal to one another.
 30. Theapparatus for low flux photocatalytic pollution control of claim 25 ,further comprising: second low flux longitudinal lamps positionedparallel to each other; second stage photocatalytic reactors, positionedparallel to each other, each of the second stage photocatalytic reactorsincluding each of the second low flux longitudinal lamps for convertinga second portion of the target pollutant passing.
 31. The apparatus forlow flux photocatalytic pollution control of claim 25 , furthercomprising: second low flux longitudinal lamps positioned parallel toeach other; second stage photocatalytic reactors, positioned parallel toeach other, each of the second stage photocatalytic reactors includingeach of the second low flux longitudinal lamps for converting a secondportion of the target pollutant passing; and third low flux longitudinallamps positioned parallel to each other; third stage photocatalyticreactors, positioned parallel to each other, each of the third stagephotocatalytic reactors including each of the third low fluxlongitudinal lamps for converting a third portion of the targetpollutant passing therethrough to the pre-determined final level ofdestruction and removal efficiency (DRE).
 32. An apparatus for low fluxphotocatalytic pollution control comprising: a first stagephotocatalytic reactor having a first single low flux longitudinal lampfor converting a first portion of a target pollutant passing; and a laststage photocatalytic reactor having a last single low flux longitudinallamp for converting a last portion of the target pollutant passingtherethrough to the pre-determined final level of destruction andremoval efficiency (DRE).
 33. The apparatus for low flux photocatalyticpollution control of claim 32 , wherein each of the first stagephotocatalytic reactor and the second stage photocatalytic reactorinclude: a single jacket.
 34. The apparatus for low flux photocatalyticpollution control of claim 32 , further comprising: a second stagephotocatalytic reactor having a second single low flux longitudinal lampfor converting a second portion of the target pollutant passing.
 35. Theapparatus for low flux photocatalytic pollution control of claim 34 ,further comprising: a third stage photocatalytic reactor having a thirdsingle low flux longitudinal lamp for converting a third portion of thetarget pollutant passing therethrough.
 36. A method of low fluxphotocatalytic pollution control comprising the steps of: passing atarget pollutant into a first photocatalytic reactor, a first catalyticmedia and a second catalytic media, and at least one low flux lightsource; and converting the target pollutant that passes through thefirst catalytic media and the second catalytic media to a selected levelof destruction and removal efficiency (DRE).
 37. The method of low fluxphotocatalytic pollution control of claim 36 , wherein the passing stepfurther comprises the step of: orienting the fist catalytic media andthe second catalytic media in series to one another.
 38. The method oflow flux photocatalytic pollution control of claim 36 , wherein thepassing step further comprises the step of: orienting the catalyticmedia and the second catalytic media in parallel to one another.
 39. Themethod of low flux photocatalytic pollution control of claim 36 ,wherein at least one light source further includes: a single low fluxlight source for both the first catalytic media and the second catalyticmedia.
 40. The method of low flux photocatalytic pollution control ofclaim 36 , wherein the at least one light source further includes: afirst low flux lamp for the first catalytic media and a second low fluxlamp for the second catalytic media.
 41. The method of low fluxphotocatalytic pollution control of claim 36 , further comprising thesteps of: passing the target pollutant into a second photocatalyticreactor having at least one catalytic media, and at least one low fluxlight source; and converting the target pollutants that pass through thesecond photocatalytic reactor to a second selected level of destructionand removal efficiency (DRE).
 42. The method of low fluxphotocatalytic-pollution control of claim 41 , further comprising thestep of: orientating the first photocatalytic reactor in series with thesecond photocatalytic reactor.
 43. The method of low flux photocatalyticpollution control of claim 41 , further comprising the step of:orientating the first photocatalytic reactor in parallel with the secondphotocatalytic reactor.
 44. The method of low flux photocatalyticpollution control of claim 36 , wherein the first catalytic media andthe second catalytic media have different lengths.
 45. The method of lowflux photocatalytic pollution control of claim 36 , wherein the firstcatalytic media and the second catalytic media have identical lengths.46. The method of low flux photocatalytic pollution control of claim 41, wherein the first reactor and the second reactor have differentlengths.
 47. The method of low flux photocatalytic pollution control ofclaim 41 , wherein the first reactor and the second reactor haveidentical lengths.
 48. A method of low flux photocatalytic pollutioncontrol, comprising the steps of: passing a target pollutant into aphotocatalytic reactor having at least one organic catalytic jacket andat least one low flux light source; and converting the target pollutantthat passes through the first catalytic media at a selected level ofdestruction and removal efficiency (DRE).